Sebastián Fernández de Medrano

Director of the Royal Military and Mathematics Academy of Brussels Sebastián Fernández de Medrano
Born	24 October 1646
Died	30 March 1705(1705-03-30) (aged 71)
Allegiance	Spain
Service / branch	Spanish Army Ensign Engineer Tercio Infantry Artillery
Years of service	1661–1705
Rank	Ensign, Battle General, General Prefect, Maestro de Campo, Chief Artillery Engineer, Captain, General of Artillery
Battles / wars	Franco-Dutch War War of the Reunions Nine Years' War War of the Spanish Succession

Sebastián Fernández de Medrano (24 October 1646 – 18 February 1705) was a Spanish military leader, engineer, polymath, and scholar who served as the president and sole director of the Royal Military and Mathematics Academy of Brussels, considered the first modern military academy in Europe. Active during the reign of Charles II of Spain and briefly Philip V, Medrano held numerous titles throughout his career, including Royal Master of Mathematics in the States of Flanders, General Prefect to the King, Captain and Maestre de Campo of the Spanish Tercio, General of Artillery, Chief Artillery Engineer of the Kingdom, geographer, cartographer, inventor, author, and military architect. He played a foundational role in the development of Spanish military science and education during the late 17th century.

He is best known for founding and directing the Royal Military and Mathematics Academy of Brussels (1675–1706), the first modern military academy in Europe, which trained a generation of elite engineers and officers who shaped warfare across Spain and the Habsburg world.

Background

Sebastián Fernández de Medrano was born in Mora, in the province of Toledo, and baptized there on October 24, 1646, according to parish records. According to Antonio Rodríguez Villa, his parents, Sebastián Fernández de Mora and Isabel de Medina, were local residents of Mora. While these origins are accepted by some historians, royal privileges, the 'Geography of Medrano' map dedicated to Charles II of Spain by Medrano, allegorical tributes and later events in his life raise questions about whether he may, in fact, have been a descendant of the noble Medrano family.

According to Medrano's own accounts and the testimony of the Royal Military Academy of Brussels, he rose from humble beginnings, orphaned and without fortune, with only the limited education accessible in a small Spanish town. Although Villa claimed Medrano was introduced into military service by a noble patron from the Medrano family, Medrano himself credited Fernando Miguel de Tejada, a senior official in the Consejo de Guerra, for securing his first commission. This direct statement contradicts the Mora narrative and suggests that Medrano's advancement stemmed from lineage, merit, and battlefield recognition—not just patronage.

Villa's claim, while influential, is further complicated by the shared prominence of the Tejada and Fernández de Medrano lineages. In a separate context, Diego Fernández de Medrano, and his brother Tomás Fernández de Medrano—the author of República Mista—was described by Licentiate Salinas as a "true and legitimate descendant" of Sancho Fernández de Tejada, the famed general under King Ramiro I of Asturias. The parallel between Tomás's ancestral claim and Sebastián's own reliance on Fernando Miguel de Tejada, suggests a broader dynastic linkage between the Fernández de Medrano and Tejada houses—strengthening the view that Sebastián bore the Medrano name by right of lineage, not by borrowed patronage.

However, decades later, the historian Villa proposed in his 19th-century reprint of Medrano's works that at the age of fifteen, he traveled to Madrid under the protection of a distinguished gentleman of the Medrano family.

This nobleman reportedly brought the young Sebastián to Madrid, helped secure his entry into a military tercio, and arranged for his eventual transfer to the Spanish Netherlands, where he would begin to use the name Sebastián Fernández de Medrano. Throughout his autobiography, he never denied this name nor referenced any connection to the surname "Mora" or his purported birth in Mora. On the contrary, the name "Medrano" appears in all his official writings, dedications, engravings, and tributes, and he carried it with distinction until his death.

The surname was also recognized by King Philip V and carried by his four daughters, who bore the full surname "Fernández de Medrano" in legal and financial records—further reinforcing the enduring familial use of the name and its recognition across legal and institutional documents.

Long after Medrano's death, Rodríguez Villa also suggested that he had merely adopted the Medrano surname from a patron, implying that he was originally Sebastián Fernández de Mora. However, this claim was not supported by Medrano himself and contradicts the allegorical and poetic honors bestowed on him during his lifetime, which often emphasized his ancestry and valor as qualities inherited from Medrano lineage.

Notably, Tejada y Ramiro’s official catalog of military authors, published by order of the Ministry of War in 1856, listed him without hesitation as Sebastián Fernández de Medrano, without mention of any alternative surname or background. This authoritative listing, along with his own lifetime publications and the literary tributes of his contemporaries, supports the interpretation that Medrano was either a legitimate bearer of the name or publicly recognized as such by both his peers and the crown.

Official recognition by the Habsburg Empire

Furthermore, Medrano’s legacy as a legitimate bearer of the name was formally recognized by imperial authority. In 1723, a royal privilege issued by Emperor Charles VI—King of Spain and Holy Roman Emperor—authorized the widow of printer Henrico Verdussen to publish "las Obras de Medrano" (the Works of Medrano) exclusively in the Spanish Netherlands. The decree specifically names Medrano as the author of the collected works, without mention of any alternative identity, and legally protected their publication for six years under imperial sanction.

Aristocratic and diplomatic reach

His correspondence with an extraordinary range of high-ranking nobles, bishops, Electors, and princes further reflects the level of recognition and prestige he held under the Medrano name. The deep symbolic language surrounding Medrano's public image reached its peak in a 1700 royal allegory, which portrayed him as the embodiment of martial and intellectual excellence.

Royal allegory and Medrano's public image (1700)

Engraving from The Perfect Architect in the Art of War (1700) proclaiming his Medrano ancestry: "The blood of your ancestors, whom sacred virtue made divine, and martial valor, Fame—rightly come to you, from Medrano, the labor of a master of war."

Written by the herald in the royal court of Charles II of Spain, this elaborate allegory frames Medrano as the central figure in a cosmic contest between the gods. The poem depicts Themis crowning Medrano with a triple diadem—symbolizing mastery in law (Themis), war (Mars), commerce (Mercury), and navigation and sea power (Neptune). It is an exalted portrayal of Medrano’s intellectual and martial legacy:

To the most blind, in the army of the king, as the general prefect. Mercury, Nereus, and Mars vied for his honor, but Themis settled their disputes, declaring that whatever wealth radiated to them, MEDRANO revealed. The gods were not disappointed, and Mercury put down his arms, Mars laid aside his weapons, and Nereus presented a shield. MEDRANO laid at their feet heaps of spoils, and Themis built a triple trophy, crowning him with a triple diadem. The first crown bore the insignia of the defeated Mars, the second that of Mercury, and the third that of Neptune. Fame heard and flew, marveling at the unusual trophy, and filled the world with a thousand trumpets. God overpowered their voices, carrying the light throughout the heart and from there surpassed even the sharpest-eyed lynxes.

Sebastián’s use of the Medrano name coincided with the presence of the Fernández de Medrano family in La Rioja, and Antonio Vélaz de Medrano, 1st Marquess of Tabuérniga, who had been appointed governor of Nieuwpoort in Flanders. The Medrano name already commanded great respect across the Spanish Netherlands and Iberia, associated with royal patronage, military command, and intellectual distinction.

By carrying the name, and being honored in verse and dedication as a bearer of ancestral martial valor, Sebastián appears to have been understood—even by his peers—as a legitimate Medrano. This identification passed to his descendants, who continued to bear the Fernández de Medrano surname in noble and military circles across Spain and the Spanish Netherlands.

Medrano's family and pension

Sebastián Fernández de Medrano was the father of four daughters, Doña Catalina, Doña Bernarda, Doña Irene, and Doña Eufemia Fernández de Medrano y Saseguen. After the misfortune that befell her husband, Doña Mariana de Saseguen, originally from Alost in the Brussels diocese and daughter of Gaspar de Saseguen and Susana de Riech, moved to Spain to live with her daughter, Doña Catalina de Medrano. Catalina was married to Mr. José de Pedrajas.

His wife Mariana stayed with them until her own passing on April 3, 1719, in Madrid. She was interred in the church of the Agonizing Fathers. Throughout the tumultuous period, the wife and daughters of the distinguished general were granted a monthly pension of seventy silver escudos. This pension was disbursed by the main treasury of the Kingdom of Valencia and sourced from confiscated properties.

Poetic tributes to Medrano

Sebastián Fernández de Medrano inspired several poetic homages from fellow scholars, military officers, and disciples. These works not only reflect admiration for his intellectual and martial accomplishments, but also celebrate the mythic stature he achieved in his own time.

Sonnet by an unnamed disciple

Apollo and the Muses on Mount Parnassus, c. 1650, by Johann Christoph Storer. Held at National Gallery of Art

This dedication, composed during Medrano’s directorship, attributes his knowledge to divine inspiration, casting him as the chosen of Pallas, Urania, Vulcan, and Neptune. It reflects the scientific and navigational scope of his work:

Es Divina, o MEDRANO, tu eloquencia, Porque viendo las Musas tu cordura Que adquiras cada qual por si procura, Lo noble de las Artes y la Sciencia, y Asi Palas te dio la inteligncia Para su Mlitar Arquitecture; Y Urania de su Esphera la luz pura Para medir sus orbes con prudencia. Para este horrible incendio dio Vulcano El fuego de su fragua fulminane; Y para hallar camino al Oceano. Cartes Neptuno, Brujula y Quadrante: Con que goza la Espana por tu mano De estas ilustres Sciencias lo importante.

"Your eloquence is divine, o MEDRANO, because the muses see your wisdom and that you strive for the noblest of arts and sciences, and thus Pallas gave you the intelligence for his military architecture; and Urania from her sphere the pure light to measure her orbs with prudence. For this horrible fire Vulcan gave the lightning of his thundering forge; and to find a path to the Ocean, Neptune provided maps, a compass, and a quadrant: with which Spain enjoys through your hand the importance of these illustrious Sciences."

Sonnet by Manuel Pellicer y Velasco (1688)

Written by Medrano’s friend and student, this sonnet captures both the poetic and pedagogical aspects of his legacy. It emphasizes the breadth of Medrano's knowledge and immortalizes his intellectual contribution through classical metaphor:

A torch that, when extinguished, you shine brightly, a Sun that, amidst clouds, turn [to] your rays, Cupid of the sciences that you adorn, Eloquence and all its greatness. Just fame of immortality you deserve, And applause and fame together conspire, Reducing to the harmony of the lyre, The harmonious sphere that you present here. With eight volumes, With Spanish affection, you have enlightened the martial school, And your industrious and versatile genius soars, To that of Apollo with which you have achieved, after sailing so long without a sail, to remain crowned with sacred Daphne.

Sonnet to Medrano

Another tribute, penned by a fellow academician and preserved in an official reprint of Los Elementos Geométricos del Famoso Philosopho Euclides Megarense (1728), praises Medrano’s intellectual rigor and martial eloquence in poetic form. The work was re-published in Antwerp by the widow of Henrico Verdussen and originally dedicated to Isidro de la Cueva y Benavides, Marquess of Bedmar and General Commander of the Spanish Netherlands. The poem reflects on Medrano's mastery of the military arts, divine inspiration, and the envy his fame provoked—even from the god Apollo himself:

When your subtle pen, O great Medrano, Ceases to write of the rugged Art, With what fury Bellona inspires Mars, And lets your sharp hand rest: Seeking further praise has been in vain, For what is written here suffices, That Pallas may crown you, Without Vulcan’s fiery forge. Consider that in the end you are a man, And that you may stir Apollo’s ire, With so much inquiry—and do not be amazed— If, in vengeance and punishment, for spoils, (Envying your fame so great a name), He triumphs in the sight of your eyes.

Poetic Reflection by Chrysostomus de Monpleinchamp (1701)

This poem, composed the year before Medrano’s death, reflects on his blindness not as a limitation, but as a metaphor for transcendent vision. It evokes the image of a sage navigating celestial realms with intellectual clarity despite physical darkness:

"To Master Sebastián Fernández de Medrano, both blind and keen-sighted, in the King's Army, as the General Prefect: Veiled by clouds, the sun preserves the mortal lights, and both worlds twinkle in alternation. Similarly, Medrano, deprived of his twin eyes, wanders the House of the Sun and Uranus with his ingenious mind."

These poetic tributes reflect the extraordinary stature Sebastián Fernández de Medrano held among his contemporaries—not merely as a military leader or educator, but as a figure of mythic resonance. In the eyes of his peers, he united the disciplines of war, science, and eloquence, embodying the ideal of the soldier-scholar. Through verse, his disciples and admirers immortalized his contributions, elevating him to the ranks of timeless genius and anchoring his legacy in the literary as well as the historical canon.

'First system' of fortification (1687)

The architect, military engineer and lieutenant general Juan Martin Cermeño argued that Sébastien Le Prestre, Marquis of Vauban's well-known ‘first system’ of fortification, recognized for its orillons and curved flanks and published in a 1689 Amsterdam pirated edition, had actually been preceded by Sebastian Fernandez de Medrano's work in Brussels in his academic book "El Ingeniero Practico," published in Brussels in 1687. Medrano, who was the director of the Royal Military Academy of the Spanish Netherlands, had developed similar fortification concepts.

Cermeño noted that while Vauban might have refined ideas originally suggested by Marchi, Medrano's designs were also highly advantageous, albeit somewhat complex to implement. However, Medrano's contributions were overshadowed, according to Cermeño, by the misfortune of being Spanish and working during a period when Spain's military innovations were not as celebrated as in other eras, as noted in "La Mina" (1898).

Geographer

Illustration in "Geography or modern description of the world and its parts" (1709 edition) by Sebastian Fernandez de Medrano

The Colonel of Engineers Joaquín de la Llave held a conference to establish Sebastián Fernández de Medrano as a geographer on 28 November 1905. Colonel Joaquín de la Llave provided a comprehensive overview of the life and achievements of Sebastián Fernández de Medrano, declaring his significant contributions as a geographer and military engineer. Held to honor Sebastián's interdisciplinary impact on military architecture and geography, the conference focuses on his scholarly works and educational legacy.

Joaquín de la Llave discussed Medrano's enduring influence on the methodologies employed in military academies and his pivotal role in training engineers and military personnel. Regarding Sebastián Fernández de Medrano, Colonel de la Llave made a statement in his 1905 conference:

"His books are clear and methodical. The doctrine is presented with great precision and clarity, and therefore, as textbooks for the Academy of Brussels, they represent a considerable advancement. It is also important to note that at that time, geographic studies were very neglected. In most European countries, geography was not studied, or if it was, it was done in such an elementary way that it was far from what Medrano taught his disciples, which, while not perfect knowledge, represented a significant advancement over what had been done until then. Therefore, I believe that, without taking away the place that corresponds to him, Fernández de Medrano cannot be denied the status of a geographer, and a geographer of certain importance among ours; he represents a marked progress in Spanish geography, in its didactic part, and deserves some tribute, some consideration from the Geographical Society, which is the purpose that guided me in giving this lecture."

'Geography of Medrano' Dedicated to Charles II of Spain by Sebastián Fernández de Medrano, director of the Royal Military and Mathematics Academy of Brussels. The Latin around the neck of the lion reads: "I am the peak of the Austrian name and the twin lions, the armor of the world..."

Colonel de la Llave acknowledges Medrano's Academy and credits him with significantly enhancing military training by combining practical and theoretical education. Medrano was credited with authoring influential textbooks that combined detailed geographical descriptions with practical military applications. His works included "La Geografía ó moderna descripción del Mundo y sus partes," and "Breve descripción del mundo, ó guia geographica de Medrano" dedicated to King Charles II of Spain, which, according to Colonel de la Llave, were instrumental in advancing geographic science during his era.

A poem from the "Geography of Medrano" dedicated to Charles II of Spain by Sebastián Fernández de Medrano in 1688:

"My lord, deity of Austria, to you with sincerity, My humble chest renders adorations, And with loyal affection for offerings, Consecrates upon your altars this globe. If only, my lord, I could make it so, That yours were the variety of its regions, And expand the domain of your lions, In another that surpasses the first. I dedicate to you in [this] abbreviated volume, Trusting only in your clemency; For if I lose myself in such a vast world, Excused by blindness and by zeal, In you, Charles without Second, I will be found."

Autobiography

Sebastian Fernandez de Medrano left his own autobiography. His autobiography was later published in "Noticia biográfica de Don Sebastián Fernández de Medrano" by Antonio Rodríguez Villa, published in Madrid in 1882 by M.G. Hernandez. It is part of the Americana collection and is held in the collections of Harvard University.

Military career

From a young age, Sebastián Fernández de Medrano was drawn to royal service, beginning his military career at the age of fifteen. He participated in four military campaigns across Castilla la Vieja during 1660 and 1661, serving under the governance of the Duke of Osuna, primarily in roles stationed at simple garrisons along the frontier.

Referring to Castilla la Vieja, Colonel de la Llave suggests that Medrano participated in military campaigns across the provinces of Zamora or Salamanca.

This early exposure to military life marked the beginning of a distinguished and eventful journey in service to the Spanish crown. His commitment to military sciences led him to Madrid, where, inspired by "the whims that had taken root in my head," he prepared for an auspicious military opportunity. Sebastián recalls how this opportunity materialized in 1667, when the court was raising a new tercio of infantry destined for service in Flanders under His Majesty. Sebastián Fernández de Medrano recounts relying on Fernando Miguel de Tejada, who "had known me when I was the General Field Master in that frontier," to secure his position. He successfully became an ensign and obtained a flag in the company of Juan de Meneses.

Arrival in Flanders

Coat of Arms of the Marquess of Gastañaga (4 Quarters: Agurto, Alava, Salcedo, Medrano and Zúñiga)

In 1668, his ambitions took him to Flanders, where he joined the company of Juan de Meneses in the tercio commanded by the Master Field Marshal Lord Francisco Antonio de Agurto Salcedo Medrano, later known as the Marquess of Gastañaga and Governor and Captain General of the Habsburg Netherlands (also known as the Low Countries).

Sebastian Fernández de Medrano reflected deeply on his experiences and the influences that shaped his military career, noting the profound respect he held for the Marquess of Gastañaga, the Governor and Captain General of Flanders. Sebastián wrote:

"Since the aforementioned Lord Marquess loved the glory of the Military so much...he highly esteemed the officers of his tercio who were inclined to service and applied to everything required to acquire their good judgment."

This admiration led to a reciprocal relationship, as Medrano was "fortunate enough to earn his favor," which significantly impacted his military trajectory. Throughout his service, Sebastián was consistently involved in critical decisions, he wrote:

"The Marquess of Gastañaga always took me with him on campaigns and visits to garrisons, not making a decision without favoring my opinion."

This mentorship and collaboration continued until the death of the Marquess of Gastañaga. Despite this supportive environment, Medrano encountered skepticism from fellow officers regarding his intense focus on mathematics—a discipline he pursued with unwavering commitment, even as some deemed him “crazy” for devoting himself so fully to it. His persistence ultimately proved fruitful. Medrano acquired what he described as “a decent theoretical understanding of fortification and artillery use, as well as some practical experience in the construction of fortifications.”

His efforts stood out in a context where many foreign engineers demonstrated only superficial knowledge, a shortcoming Medrano identified through his evaluation of works commissioned by the Count of Monterrey. Reflecting on these formative years, Medrano recalled his experiences during the brief conflict following the breach of the Peace of the Pyrenees and the later Peace of Aix-la-Chapelle. These episodes, he believed, deepened his understanding of military engineering during a pivotal era in European warfare. Through his academy, Medrano trained officers and soldiers from across Europe, with particular emphasis on the Army of Flanders.

Establishment of the Royal Military and Mathematics Academy of Brussels (1675)

Flag of the Habsburg Netherlands

Sebastian Fernández de Medrano's military prowess and reputation reached notable figures such as Diego Gomez de Espinosa, Luis de Acosta Quiroga, and Joseph Manrique, influential field marshals who recognized his capabilities. During a period when these marshals were organizing regiments of "cadets," consisting of nobles or officers' sons being trained in martial arts and seamanship, Medrano's expertise became particularly valuable. His renown led them to propose to the Duke of Villahermosa the establishment of a military academy to modernize military training:

"...the field marshals informed the Duke of my ability and suggested that instead of granting me leave [to Spain], he should establish a military academy for the army, where we could acquire a skill that was so lacking in the new way of waging war. The Duke agreed with this suggestion and immediately summoned me. He said that it was good timing for me to come to Spain, as he intended to establish a martial seminar for the army, and that he wanted me to be the director."

The Duke of Villahermosa's request

Coat of arms of the Duchy of Villahermosa

Sebastián Fernández de Medrano’s return to Spain aligned with the strategic vision of the Duke of Villahermosa, who sought to establish a "martial seminary for the army." Although Medrano initially expressed reluctance—citing personal doubts about his ability to manage such a complex and demanding undertaking—the Duke’s persistence and confidence in his abilities ultimately persuaded him. Accepting the challenge, Medrano assumed the directorship of the new academy, stepping into a decisive role that would shape the future of Spanish military education. The Royal Military and Mathematics Academy of Brussels, considered the first modern military academy in Europe, had originally been founded by Medrano in 1675 in Brussels, capital of the Habsburg Netherlands, at the request of Carlos de Aragón de Gurrea, 9th Duke of Villahermosa. Its creation responded to an urgent need to address the shortage of trained artillerymen and military engineers within the Spanish Tercios.

Medrano wrote in his autobiography:

He [the Duke of Villahermosa] said that it was good timing for me to come to Spain, as he intended to establish a martial seminar for the army, and that he wanted me to be the director. I excused myself, saying that I did not feel capable of undertaking such a difficult task, but he insisted, saying that he knew what I was capable of, and that when he was the general of the cavalry during the siege of Audenarde, he had seen me hit fourteen point-blank shots from a cannon (which I had done by order of the Duke of Montalto, who was the field marshal in charge of the trenches). With these circumstances, I could not refuse and accepted the offer.

Director of the first modern military and mathematics academy in Europe

Following the establishment of the Royal Military and Mathematics Academy in 1675, Sebastián Fernández de Medrano swiftly consolidated his reputation as a pioneering figure in military education. His directorship attracted a "large number of officers from all ranks," signaling the academy’s rapid rise in prestige. This momentum was reinforced by the publication of his treatise Rudimentos Geométricos y Militares (Rudiments of Geometric and Military Principles), which became a foundational component of the academy’s curriculum. Celebrated for its clarity and pedagogical accessibility, the work was widely embraced. Reflecting on its reception, Medrano remarked that "within a year, many had benefited from the new method I had established, which was designed to be so straightforward that even the least intelligent learned from it very quickly."

By 1688, the Army of Flanders—strengthened by the training provided at Medrano’s academy and commanded by the Marquess of Gastañaga—had reached a force of 25,539 officers and men. By the following year, this number had increased to 31,743, marking the army’s peak strength during the Nine Years' War. The educational foundation laid by Medrano played a pivotal role in shaping the technical proficiency and leadership capacity of these troops.

Inspiration

Juan Domingo de Zuñiga y Fonseca, Count of Monterey

Sebastián Fernández de Medrano drew inspiration from Juan Domingo de Zúñiga y Fonseca, Count of Monterrey and President of the Supreme Council of Flanders. Recognizing the Count’s leadership and commitment to military advancement, Medrano acknowledged his influence in correspondence. In a letter addressed to Juan Domingo de Zúñiga y Fonseca, he writes:

...seeing the generosity with which Your Excellency favored the diligent; it ignited in me such ambition for glory, to unite the practice of my services with the theoretical knowledge of the Mathematical Disciplines belonging to the Artillery. Supported by this, His Majesty granted me the establishment of the New and Royal Academy, of which I am the Director. Through my presence and writings, which I have published on these matters, many individuals capable in Military Architecture have emerged, not only for His Majesty's borders but also for those of the Allied Princes, who have made use of them. It is well known that in the past we had to seek them from abroad.

Benefactor of the armies in Europe

Director Sebastián Fernández de Medrano exerted a profound influence on the generals and armies of Europe through his academic leadership and military expertise. Reflecting on this impact, he writes:

... upon being informed by my generals, I owed to their magnanimity the noble attribute of being named in their Royal Dispatches as a benefactor to their armies.

Captain of Tercio

The widespread renown of the academy and the adoption of Medrano’s instructional methods earned him considerable distinction. In recognition of his service, Carlos de Aragón de Gurrea, 9th Duke of Villahermosa and Governor and Captain General of the Netherlands, Burgundy, and Charolais, entrusted Medrano with the command of a tercio infantry company. This honor was formally confirmed with the issuance of a royal patent on 30 April 1679:

...Considering these and other good qualities required and desirable for this position in you, Don Sebastian Fernandez de Medrano, taking into account how well you have served His Majesty (...) I have chosen and appointed you as the Captain of the said company, in the place of the said Don Juan de Garcerán, giving you and granting you (...) the said Tercio.

Duke of Villahermosa and Charles II of Spain

Carlos de Aragón de Gurrea y de Borja

To secure the continued success of the military academy he had founded, His Excellency Carlos de Aragón de Gurrea, 9th Duke of Villahermosa, submitted a formal report to King Charles II detailing the institution’s accomplishments since its inception. Emphasizing the indispensable role of Sebastián Fernández de Medrano in leading this pioneering educational initiative, the Duke strongly recommended that Medrano be permitted to resume his directorship, underscoring the strategic value of his contributions to the improvement of the royal army. In response, King Charles II issued a royal mandate on 16 November 1679 from Burgos, endorsing the Duke’s proposal and authorizing Medrano’s continued service.

The order explicitly affirmed the necessity of Medrano’s leadership in the interest of strengthening the Crown’s military capacity:

With regard to what you report in your letter about the convenience that will result from Captain Sebastian Fernandez de Medrano continuing to teach Mathematics in those states, and to this end assigning him the salary of a live captain and providing him with his company, I have agreed to what you propose.

The King further directed the Duke to implement the appropriate measures to ensure that Medrano received his captain’s salary and command of his company, explicitly overriding any prior orders that might impede this arrangement.

Beyond the individual case, Charles II emphasized the strategic importance of cultivating military education, declaring that efforts must be made to “favor greatly those who dedicate themselves to this profession, as it is necessary to have qualified individuals in this field everywhere.” This royal endorsement affirmed the Crown’s recognition of specialized military training as essential to the strength and preparedness of the Spanish armed forces, and highlighted Medrano’s role as a leading figure in advancing that vision.

Achievements

Allegorical engraving of Pallas Athena and Mars honoring Sebastián Fernández de Medrano, symbolizing his mastery of wisdom and war: "Mars offers, and Pallas presents to you the teachings of Medrano." From El Ingeniero Práctico (1696), dedicated to Joseph Ferdinand of Bavaria.

Recognizing the substantial progress achieved by the Royal Academy of Mathematics, the Duke of Villahermosa once again expressed his admiration for Sebastián Fernández de Medrano's efforts in a formal letter to King Charles II. In his correspondence, dated Brussels, 18 July 1680, the Duke commended Medrano’s dedication, scholarly rigor, and the measurable impact of the academy in elevating Spain’s military capabilities. He underscored how the institution, under Medrano’s leadership, had notably strengthened the Crown’s artillery and engineering corps, contributing to the broader goals of national defense and imperial strategy. The Duke wrote in Brussels, on 18 July 1680:

Sir, when I established the Royal Academy of Mathematics in these States by your order and approval, I also informed you of the choice I had made of Captain Sebastian Fernandez de Medrano to teach this subject to the officers and soldiers of the army. In the limited time that the military have attended, many have become very proficient in the understanding of the arts that make a soldier capable in his profession... the proof of having already sent some engineers to other armies, who with the experience previously acquired and the theory of mathematics, have advanced in such a way that it has been achieved that today Your Majesty no longer needs to rely on engineers and artisans from other nations, which carries so much risk of confidence, having expert Spaniards in these matters.

This training included essential military skills such as fortification design, geometric calculation methods like squaring, and the effective use of artillery. The Duke of Villahermosa emphasized that the success of the academy provided Spain with strategic self-sufficiency in military engineering. In a letter dated 18 July 1680 from Brussels, the Duke urged King Charles II to formally recognize and reward Sebastián Fernández de Medrano's contributions, writing on July 18, 1680:

I must implore Your Majesty to deign to bear this merit in mind in order to qualify it with remuneration, as it is such an effective means for the advancement of the arts that lead to Your Majesty's Royal service to signalize them in the reward and prize of their sovereign justification and greatness.

Contributions to the field of military sciences

Geographic Map of a New Description of the Great River and Empire of the American Amazons. Spanish Leagues, outlined by Joseph de Mendoza Sandoval, Disciple of the Author. "Dedicated to His Excellency Lord Count of Fuensalida; by the Battle General D. Sebastian Fernandez de Medrano, Director of the Royal and Military Academy of the Low Countries" (Image provided by Gallica)

Encouraged by royal support and institutional success, Medrano deepened his commitment to the advancement of military science. He began publishing numerous works on topics such as fortification, geometry, battalion formation, artillery deployment, and mortar use. His scholarly range also extended to geography and navigation—pursuits that he personally financed, reportedly exhausting his wife’s inheritance in the process. These efforts resulted in the formation of a highly trained corps of military engineers whose expertise was in high demand across Europe. As Medrano himself noted:

"As a result, a great number of engineers were trained, and His Majesty and later the Holy Roman Emperor and Princes of the League requested their services for all the borders of their dominions." The quality and effectiveness of these engineers were such that previously, "we had to beg for engineers because there were no subjects who understood this field."

Among Medrano’s most distinguished pupils was an engineer named Reysemberg, who went on to serve as General Engineer to the Emperor, while another became an engineer in the service of King James II of England. Their reputations were solidified by their exemplary performance during major military campaigns. Medrano recalled, "For the sieges of Mainz and Bonn, the Duke of Lorraine requested their services, and they worked so well that they earned the applause of that great champion and the Duke of Bavaria, as stated in a letter from the Elector of Trier on October 2, 1689."

Medrano accompanies the Marquess of Gastanaga

Medrano's personal involvement in military operations continued as he accompanied General Field Marshal Francisco Antonio de Agurto Salcedo Medrano on visits to Cologne, Bonn, Trier, and Koblenz, he recalls his active role in applying and promoting military engineering across Europe.

Portrait of the Archbishop-Elector of Trier

During a visit to Koblenz, Sebastian Fernández de Medrano encountered an unexpected recognition of his expertise. Johann Hugo von Orsbeck, Archbishop-Elector of Trier, upon learning of Medrano's presence through officers who had previously been his students, sought his expert opinion on the fortifications of Koblenz and its prominent castle, Ehrenbreitstein.

Aerial photograph of the Castle of Ehrenbreitstein, Koblenz, Rhineland-Palatinate, Germany

Initially, Medrano expressed reservations, modestly stating, "I replied that I did not have enough knowledge in the military to give an opinion on fortification," however, the Elector persisted by recalling Medrano's credentials as the Director of the Royal Academy of Brussels and expressing trust in his judgment due to his reputation. Medrano wrote:

He [von Orsbeck] insisted, saying that I was the Director of the Royal Academy of Brussels and that, being an Austrian prince, he could trust my judgment.

Encouraged by this confidence, Medrano then offered his recommendations for necessary repairs and improvements to the fortifications. The discussions concluded with an agreement that Medrano would recommend the most capable individuals for the fortification work when the Elector requested.

Medrano's disciple Juan de Ortega

Later, Sebastián Fernández de Medrano sent one of his most promising students, Don Juan de Ortega, to support the Archbishop-Elector of Trier, Johann Hugo von Orsbeck, during the siege of Mainz. Ortega was killed in action. The Duke of Lorraine mourned the loss, reportedly remarking that "a valuable man had been lost." The Archbishop-Elector, who had previously sent two of his own subjects to train under Medrano at the Brussels Academy, expressed his admiration for Ortega’s skill and training. In a letter dated 2 August 1689, Orsbeck praised Ortega’s contributions to the fortifications of Trier and underscored the influence of Medrano’s instruction: "He could have given, with time, signs of great service to the King, his master, where the glory would always redound to his first Director [Sebastián Fernández de Medrano]."

In a letter dated 2 August 1689, Johann Hugo von Orsbeck, Archbishop-Elector of Trier, expressed deep appreciation for the training provided by Sebastián Fernández de Medrano, Director of the Royal Military and Mathematics Academy of Brussels. He praised the military contributions of Medrano’s disciple, Juan de Ortega, whose engineering expertise had significantly aided the Archbishop’s fortification efforts. Orsbeck lamented Ortega’s death in action during the siege of Mainz, recognizing his promise and potential for distinguished service. He noted that Ortega's achievements reflected the quality of instruction he had received under Medrano, whose mentorship was also acknowledged by other senior military leaders such as the Duke of Lorraine.

Savoyard commendation

Sebastian Fernández de Medrano recalls a notable instance where a disciple of his, appointed to the siege of Casal di Monferrato, earned the commendation of the Duke of Savoy. This success, Medrano explains, was a direct result of his extensive firsthand experience with generals during various campaigns, notably up to the Peace of Nimeguen. During these campaigns, Medrano wrote:

I had the opportunity to observe, acquire, and personally demonstrate everything pertaining to the art and science of engineering.

Loss of eyesight

"To Master Sebastián Fernández de Medrano, both blind and keen-sighted, in the King's Army, as the General Prefect: Veiled by clouds, the sun preserves the mortal lights, and both worlds twinkle in alternation. Similarly, Medrano, deprived of his twin eyes, wanders the House of the Sun and Uranus with his ingenious mind."

Despite achieving much in his field, Medrano's relentless dedication took a toll on his health, leading to the loss of his sight:

Although I was later unable to continue participating in campaigns due to losing my sight from tireless study and work, heaven increased my spiritual vision to continue with the same and even greater fruit of serving the king by directing the Royal Academy, from which so many engineers have emerged and various works of curiosity, ease, and usefulness have been published for my disciples and for the public.

However, he poetically notes that this physical limitation only enhanced his "spiritual vision," enabling him to continue his work with even greater determination. He shifted his focus towards directing the Royal Academy, where he successfully mentored numerous engineers and oversaw the publication of various significant works that contributed to the field.

Salary payments

Medrano's efforts and the lasting impact of his academy were well documented and frequently reported to the crown by his superiors. Aware of the challenges posed by his advancing blindness and his inability to personally oversee financial matters, King Charles II extended royal clemency to ensure Medrano’s continued service. On 20 May 1688, the King issued a formal order addressing the issue of delayed salary payments and reaffirming Medrano's stipend as Captain and Director of Mathematics.

The directive, addressed to the Marquess of Gastañaga, stipulated that Medrano was to receive his monthly salary of 500 escudos promptly and without bureaucratic impediment. The King emphasized that this stipend was to be treated as "a fixed and ordinary burden, so that he may receive it without any further requirement than his payment order." He praised Medrano’s "singular merits" and the unmatched contributions of the Royal Military and Mathematics Academy, noting that its utility was "without equal and cannot be exemplified by any other."

Appointment as Maestro de Campo (1689)

The following year, on May 18, 1689, in acknowledgment of Medrano's two decades of service in various military roles and his exceptional leadership at the military academy, King Charles II awarded him the highest rank of the Maestre de Campo of Spanish Tercio:

Don Carlos, by the grace of God, King of Castile, of Leon, of Aragon... etc. In consideration of what you, Don Sebastian Fernandez de Medrano, have served me for twenty years in my army of Flanders, with the ranks of soldier, live and reformed ensign, officer of the Artillery, and captain of Spanish infantry, and for currently serving as Director of the military Academy established in that army, with particular dedication, diligence, and universal benefit of the profession: I have decided to grant you the rank of Maestre de Campo of Spanish Infantry, so that you may continue in your service with greater distinction, without this serving as an example for any other person: Therefore, I charge and command ... that you be recognized, respected, and acknowledged as such Maestre de Campo of Spanish Infantry ... and that the hundred escudos per month for your maintenance that you currently receive and are assigned in the almodiacion ... continue to be granted to you, so that you do not fail to attend to an employment so necessary and so much in my service ... Given in Buen Retiro on May 18, 1689. - I, the King

King Charles II of Spain's decree assured the continuation of his maintenance allowance of one hundred escudos per month. This promotion was meant to enable Sebastián Fernández de Medrano to serve with greater distinction.

Letter from the Marquess of Gastañaga

Portrait of Francisco Antonio de Agurto Salcedo Medrano by the engraver Richard Collin.

In a letter dated 31 October 1691, the Marquess of Gastañaga, Don Francisco Antonio de Agurto Salcedo Medrano, advocated on behalf of Sebastian Fernández de Medrano to King Charles II of Spain:

The benefit that Your Majesty's service is experiencing is evident, for when there was a shortage of Spanish engineers in Your Majesty's armies, Don Sebastian has produced so many and such distinguished disciples, officers and soldiers of this army, not only in the art of fortifying, squadroning, using artillery, fire tricks, how to throw bombs and carcasses (a type of incendiary bomb), but also in what concerns navigation, that Your Majesty can avail yourself of all those that you need. He has published at his own expense eight books, all related to these military arts, with great clarity for the shortest teaching and understanding of the disciples, which has given him so much credit among foreigners that many princes desire his disciples and send subjects to his Academy to learn from him...

Brief Description of the World and Its Parts (1686) dedicated to the Marquess of Gastañaga

The Marquess of Gastañaga praised Sebastián Fernández de Medrano’s growing merit and the consistent excellence he demonstrated in both his military service and academic leadership. He highlighted Medrano’s "zeal' and "valor," not only in military engagements but also in his steadfast devotion to the mathematical sciences. As Master Director of the Royal Military and Mathematics Academy of Brussels, Medrano was credited with significantly strengthening the Spanish military by remedying the chronic shortage of trained engineers and officers.

Through rigorous instruction in fortification, artillery, navigation, and related disciplines, Medrano trained a generation of distinguished soldiers and engineers. He also published eight technical works at his own expense, which were commended for their clarity, accessibility, and practical value—earning him international recognition. Despite suffering blindness due to years of intense study and service, Medrano continued to fulfill his duties with the same "fruit, ardor, and zeal" as before. Aware of his physical challenges and the needs of his large family, the Marquess of Gastañaga strongly recommended continued royal support for Medrano, arguing that such favor would be a just reflection of the King’s "royal benevolence and greatness."

Royal favors from the King

Sebastián Fernández de Medrano's continued dedication and exemplary service were rewarded with further royal favor when King Charles II approved an increase in his monthly salary by forty escudos. In recognition of both Medrano’s professional achievements and the sacrifices borne by his family, the king extended this favor to Medrano’s wife and four daughters. The decree included a succession clause, allowing the beneficiaries to inherit the pension successively until only one remained. Issued in Madrid on July 14, 1692, this royal concession affirmed Medrano’s long-standing service and underscored the exceptional value of his contributions to the Spanish military, particularly through his expertise in mathematics and engineering.

Testimony of the Elector of Bavaria

Medrano's dedication to the Elector of Bavaria (El Ingeniero práctico, 1696); the illustration reads: "Mars offers, and Pallas presents to you the teachings of Medrano. These are the deeds of your fatherland; may they be your martial offspring."

In one of his most eloquent dedications, Sebastián Fernández de Medrano addressed a sonnet to Joseph Ferdinand of Bavaria, the young Electoral Prince who symbolized Habsburg hopes for dynastic unity in Europe. This poem appears as the prologue to one of Medrano’s academic volumes and exemplifies the Baroque fusion of courtly praise, martial imagery, and scientific ambition. Framing his military treatise as a humble but noble gift, Medrano invokes both Pallas Athena and Mars to sanctify the science of military architecture and offer it to the Bavarian prince as a legacy of imperial wisdom and protection. The sonnet reads:

To the Most Serene Lord Joseph Ferdinand, Electoral Prince of Bavaria Sonnet Pimpolio of Bavaria, German Sun, A gift such as this my pen dares to offer, Though poor—and my own—it does not deserve To be held worthy in your exalted hand. But it is your heroic heart, so humane, That rejects it not, but grants it grace and compassion; Because whatever my faults may be, It merits your sovereign protection. It is from Pallas, this burning Architecture, And though briefly set forth in this volume, O Prince! Mars himself safeguards it. The Region is vast and far-reaching, And to raise up Bavaria to such height, That the whole world may find it without peer.

As the Most Serene Elector of Bavaria had seen Medrano's disciples work in Hungary and Germany, he informed His Majesty shortly after he had taken over the Government of Flanders, in the following letter:

Sir, the Field Marshal Don Sebastian de Medrano, Director of the Royal Academy of Mathematics in these Kingdoms, is a person of such qualities and services that Your Majesty is not only aware of them through the reports and information that the Generals and Officers of this army have provided, but also through the very effects that his ingenuity and application have benefited the Royal service of Your Majesty. So, even though I can omit the detail of repeating to Your Majesty what convinces me of the quality of Don Sebastian's merits, I do not hesitate to bring them to Your Majesty's gracious attention so that you may keep them in mind on the occasions that arise to reward them, being certain that not only will it be a worthy exercise of Your Majesty's Royal justification, but also the most useful application, as it will serve to invite encouragement and imitation. God save Your Majesty as I need. Brussels, January 26, 1694. - Maximilian II Emanuel, Elector of Bavaria

Appointment as Battle General (1694)

This representation by the Elector of Bavaria was so effective that, accompanied by others at that time from the Lord Prince of Vaudemont and Marquess of Bedmar, and continuing to justify His Majesty, he honored Medrano again in 1694 (By Royal decree of March 17th) with the rank of Battle General. Having gone to thank His Serene Highness for the favour he had shown him, Medrano found that he had been promoted without the corresponding salary for the rank, and the Elector of Bavaria was surprised by this circumstance, having believed that the promotion came with a salary, based on his good offices with His Majesty in favour of his services. The Elector of Bavaria immediately ordered Sebastián to draft a Memorandum for the King and take it to him. When he executed it, it was handed over to His Majesty on May 20 of the same year with the following representation from Maximilian II Emanuel, Elector of Bavaria:

Maximilian II Emanuel, Elector of Bavaria

Sir, the Sergeant General of Battle Don Sebastian Fernandez de Medrano, Director of this Royal Military Academy, has asked me to pass on to Your Royal hands the attached Memorandum, in which he requests that Your Majesty be pleased to grant him the salary of Sergeant General of Battle for the reasons he presents; and since I find them very worthy of Your Majesty's Royal clemency, both because of the large family and expenses he has while continuing to direct the Academy, I must hope that Your Majesty will continue to honour him by granting him the favour he requests. God save... etc.

As a result, His Majesty granted Sebastián Fernández de Medrano a monthly salary of three hundred escudos, which belong to the rank of General de Batalla, and to continue in His Royal decree the charity granted to his wife and daughters, ordering that the said three hundred escudos be paid to him and his family through the same means and in the same manner as the previous one hundred and forty escudos. Medrano wrote:

...this singular circumstance could not serve as an example for others, as I alone was judged to be of general benefit to His armies, a circumstance that I have in all my decrees, and with which the payment to me and my family has always continued.

Letter from the Prince of Vaudemont (1696)

Charles-Henri de Lorraine, prince de Vaudémont.

Motivated by His Majesty's recent demonstrations of generosity and support, Sebastián Fernández de Medrano remained unwavering in his commitment to the Academy. He worked diligently to make the sciences more accessible, continually refining his teaching methods to ensure clarity, efficiency, and comprehension among his students. Medrano’s efforts did not go unnoticed. Recognizing both his tireless dedication and the measurable benefits his instruction yielded in service to the Crown, several high-ranking officials—including the Elector of Bavaria, the Marquess of Bedmar, and the Prince of Vaudémont—found it fitting to inform His Royal Highness of the Academy’s growing significance. This recognition is exemplified in a letter sent from Brussels on January 20, 1696, by Charles Henri of Lorraine, Prince of Commercy and Prince of Vaudémont:

...although on different occasions Your Majesty has shown appreciation for the intelligence, rightly justified by the reports and information that have been presented to Your Majesty about the person and qualities of Sergeant General of Battle Don Sebastian Fernandez de Medrano, director of the Royal Academy of Mathematics in this Court, and although the transcendent benefit that his intellect and abilities bring to Your Majesty's royal service needs no further qualification than that which he already has in this army and in all the courts of Europe, I have nevertheless thought to add to the many and authoritative declarations that endorse his proficiency in all the subaltern faculties of mathematical science.

Appointment as General of Artillery

Medrano continued his work at the Academy with unwavering dedication until the final years of the 17th century. By 1699, following a lifetime of distinguished service and shortly before the death of King Charles II, he began formally petitioning for elevation to the rank of General of the Artillery—a title he believed was commensurate with his merits and long-standing contributions. His request received favorable attention from key members of the Council of State, both during the monarch’s final months and in the immediate aftermath of his passing. This support is clearly reflected in a letter dated June 18, 1699, in which Lord Cardinal wrote:

...If the reward for your useful and commendable work depended on my discretion, you would have the benefits you deserve, and if I were in the Court, I would be your agent in the request for the rank you are seeking, because, as the King, whom God protects, has foreseen and I know, you set an example for no one else, and I promise that you will achieve what you desire.

In a similar manner, prominent figures including the Count of Aguilar, the Count of Monterrey, the Duke of Medina Sidonia, the Count of Fuensalida, the Marquis of Casteldosrius, Antonio de Ubilla, and Crispin Gonzalez Botello, Secretary of State, wrote almost the exact same thing.

Salary under King Philip V of Spain

Coat of arms of Philip V, King of Spain

Following the ascension of King Philip V, both the Elector of Bavaria and the Marquess of Bedmar renewed their endorsements of Sebastián Fernández de Medrano, submitting to the new monarch the same commendations they had previously presented to his predecessor. Medrano himself includes in his writings two extensive letters of recommendation, dated 2 March and 21 July 1701, in which the Elector and the Marquess reaffirm the director’s merit, fidelity, and service to the Crown.

During this transitional period, as a new governmental structure was being established, a general suspension of salaries for generals and ministers was enacted by royal order. Yet an explicit exception was made for Sebastián Fernández de Medrano, Director of the Royal Military and Mathematics Academy and General of Battle, allowing him to continue receiving his salary without interruption.

This exemption was formalized in a royal decree issued on 20 March 1701, which instructed the Council of Finances to maintain his remuneration and preserve the status quo. Later that year, upon learning of broader fiscal adjustments in Flanders—including a universal reduction in ranks and salaries—Medrano received assurances from the Marquess of Gastañaga, Don Francisco Antonio de Agurto Salcedo Medrano Zúñiga.

In a letter dated 22 September 1701, Gastañaga informed Medrano that, despite these sweeping reductions, his own salary and emoluments would remain intact. The decision was supported by those in government who recognized his distinguished service and justified continued support. In response, Medrano wrote to the Marquess of Bedmar to reaffirm his loyalty and to ensure the continuation of Bedmar’s patronage. Bedmar advised him to prepare a formal memorial, which was submitted—following review by the Master General of the Field, the Prince of Tserclaes—to King Philip V.

This representation, dated 6 January 1702 and sent from Brussels, resulted in the king’s confirmation of the exceptional arrangement. As Medrano later recorded:

Our Lord Philip V, conformed with said representation, he confirmed the privilege and uniqueness with which I received my salary along with my family.

King Philip V clearly stated in his Royal Decree:

I agree with the consultation of the Council of State and the Count of Monterrey regarding the salary of Don Sebastian Fernandez de Medrano, and give the necessary orders to execute it, both to the Marquess of Bedmar and as long as it does not oppose any others granted by King Christianissimo and my grandfather.

Continuing his support, the Marquess of Bedmar sought to secure the same favorable arrangement for Medrano under Philip V. He instructed Medrano to coordinate with the Spanish Ambassador in France, the Marquis of Casteldosrius, to reinforce the recommendation. In response, Medrano submitted a memorial to His Most Christian Majesty, thereby contributing to a broader diplomatic initiative aimed at preserving the exceptional salary provisions that recognized his contributions to military education and service.

Endorsement by the Marquess of Casteldosrius

In his communication dated April 7, 1702, the Marquess of Casteldosrius informed Medrano that efforts had been made with His Most Christian Majesty to ensure the continuation of Medrano's salary and privileges. Following this, the Marquess of Bedmar acted to enforce these directives, including a copy of the decree in the memorial Medrano presented, thus securing the arrangements. Regarding this process, the Marquis of Casteldosrius wrote to Lord Sebastián Fernández de Medrano:

"My Lord, in accordance with what I previously informed Your Lordship... His Most Christian Majesty has instructed his Ambassador in Spain to recommend Your Lordship's person and merits to the King, Our Lord, so that he may be pleased to issue orders for Your Lordship to receive your salary as before and for Your Lordship's wife to retain the granted grace of enjoying half of it after her days."

Death (1705)

He experienced a stroke in 1704 that severely impaired his speech and memory, to the extent that he could no longer remember the prayers he usually recited with devout Christian faith. This tragic incident, along with his earlier loss of sight, left him in a profoundly sorrowful and lamentable condition until his death on February 18, 1705, in Brussels. He was laid to rest in the church of the Discalced Carmelites in the same city, which is part of the collegiate and parish church of San Miguel de Gudile.

Inventor

El Perfecto Artifcial Bombardero y Artillero by Sebastian Fernandez de Medrano (1699)

In his work "Perfecto bombardero," published in 1699, Don Sebastián Fernández de Medrano claimed to have invented a unique and innovative method for constructing the chamber of mortars, introducing what he called the "pear" shape. He considered himself the inventor of this design and believed it to be significantly important.

The Sargent General of Battle, Don Sebastián Fernández de Medrano, director of the Royal Military and Mathematics Academy of the Low Countries in Brussels, introduced his own variation of the proportional method in fortification in order to enhance the structures balance and defensive capabilities by precisely dividing inner sides and adjusting proportions, especially for pentagons, to improve fire coverage and minimize vulnerabilities, and boost the fort's defensive effectiveness and resilience. Medrano's approach split the inner side into five parts, allocating one segment to each demigorge and determining the lines of defense by drawing a line perpendicular from the midpoint of the curtain, measuring half the length of the demigorge.

The bastion boundaries were established along the defense lines at a distance equal to 1 1/10 times the length of the curtain. For pentagonal designs, he divided the half-side into six parts, with the demigorge spanning three parts, and positioned the perpendicular line at the midpoint of the curtain. The bastion's edge was then set at a distance equivalent to 1 1/7 of the curtain's length. He also explained how to use tables or a proportional compass for fortification design.

Euclids Elements

In his textbook "The first six books, eleven, and twelve, of the Geometric Elements of the famous philosopher Euclid of Megara," (1701) Medrano expands on Euclid's propositions, such as the conditions for congruence of triangles, stating, "Si dos triangulos tienen los dos lados del uno, iguales a los dos del otro, cada uno a suyo, y los angulos comprendidos entre estos lados fueren iguales: el tercer lado será igual al tercero" (If two triangles have two sides of the one equal to two sides of the other, each to its own, and the angles included between these sides are equal, then the third side will be equal to the third). Medrano advanced the pedagogical approach to teaching Euclid's elements.

In 1687, "El Ingeniero" (The Engineer), a book already quite complete in the field of fortification, containing in its second volume the study of Geometry and Trigonometry as necessary for solving a variety of problems related to the drawing of plans and calculations for the construction of fortifications.

Royal Academies of Barcelona, Oran and Cueta

Sebastian's academy had a significant legacy and impact on the formation and progress of the Royal Military Academy of Mathematics in Barcelona during the 18th century. In the late 17th century, plans were made to move the Royal and Military Academy of Mathematics from Madrid to Barcelona. Sebastián Fernández de Medrano was appointed as the general director of the academy.

The Royal and Military Academy of Mathematics of Barcelona

After deciding to establish the Royal and Military Academy of Mathematics of Barcelona, the council of war sought guidance from Sebastián Fernández de Medrano on how he had structured his academy in Brussels, intending to replicate it in Barcelona. Unfortunately, Medrano died in 1705. Before his death, he had developed an outline for the future Academy of Mathematics in Barcelona, which he submitted to the king. Consequently, the establishment of the Royal Military Academy of Mathematics in Barcelona was authorized by a Royal Decree from King Charles II on January 22, 1700.

The Royal and Military Academy of Mathematics of Barcelona was established following Medrano's model, and on January 22, 1700, a royal decree was issued to start the academy. On August 12, 1701, the implementation of Medrano's guidelines was officially ordered for the Barcelona Academy. Medrano's academic outline was published in a document titled "Formula with which the Sergeant General of Battle, D. Sebastián Fernández de Medrano, established by order of His Majesty the new and Royal Military Academy of which he is the Director." This occurred on January 22, 1700, the same day His Majesty issued a decree to establish the Military Academy in Barcelona and instructed that notices be posted in the War Secretariat to recruit teachers.

Books

After Medrano's death and after the States of Flanders were no longer part of the Spanish domains, several editions of his works were published in 1708, 1709, 1728, and 1735. Henrico and Cornelio Verdussen, publishers in Antwerp, printed these works using the privilege transferred to them by Lamberto Marchant of Bruges, which had been renewed and confirmed by Philip V in 1708. Additionally, some of the works published in Antwerp during the Austrian domination were dedicated to Philip V himself.

Sebastián Fernández de Medrano's books focus on geometry, artillery practice, engineering, architecture, geography, and exploration. A chronological list of Sebastián Fernández de Medrano's academic books:

• "New invention and method of squaring the circle, not by reason of the diameter to the circumference, but by known parts within the same circle" by Sebastian Fernandez de Medrano 1676. Dedicated to Don Carlos de Aragón de Gurrea, 9th Duke of Villahermosa and published in Brussels by Juan Dandijn

• "Rudimentos geométricos y militares, que propone al estudio y aplicación de los Profesores de la milicia" (Geometric and Military Rudiments, Proposed for the Study and Application of Military Professors) - Published in Brussels under the patronage of the Duke of Villahermosa, 1677.

• "El práctico Artillero" (The Practical Artilleryman) - First published in Brussels, 1680. - The work was reprinted multiple times and inspired the subsequent publication.

"El Ingeniero primera parte, de la moderna architectura militar" by Sebastian Fernandez de Medrano 1687, dedicated to Francisco Antonio de Agurto, 1st Marquess of Gastañaga

• "The engineer: first part, of modern military architercture. Divided into two volumes, which contain five books; the first deals with Regular and Irregular Fortification, and the views of the main authors who wrote about it. The second, on the Speculation of each of its Parts. The third on the Construction of Walls, and their Materials. The fourth on the Site, and Defense of a Fortress. And the fifth, which is the second volume, on Practical Geometry, Trigonometry, and the use of the Rule of Proportion." Published in Brussels in 1687, dedicated to Francisco Antonio de Agurto, 1st Marquess of Gastañaga.

• "The Perfect Architect in Military Art" - A corrected reprint of "The Engineer" from 1687, published in Brussels, 1700 and dedicated to the Duke of Medinaceli. There is a reprint from 1738. There is also a reprint from the year 2000.

• "Breve descripción del mundo, ó guia geographica de Medrano" (Brief Description of the World, or Geographical Guide of Medrano) - Published in Brussels by Lamberto Marchant in 1688 and dedicated to Charles II of Spain and the Marquess of Jodar. A second copy exists that was translated into french in the same year by Jean Leonard and dedicated to the 1st Marquess de Gastanaga, Francisco Antonio de Agurto Salcedo Medrano. A third edition was made and dedicated to King Philip V of Spain, published in 1702.

• "New Description of the World, and Its Parts, Divided Into Three Books" Published in Brussels in 1690 and dedicated to the Marquess of Gastanaga.

• "El Perfecto bombardero y práctico artificial" (The Perfect Bombardier and Practical Artificial) - Dedicated to the Marquess of Bedmar and published in Brussels, 1691.

"El Ingeniero práctico" (The Practical Engineer) French edition - Published in Brussels 1696. Dedicated to Maximilian II Emanuel, Prince Elector of Bavaria

• "El Ingeniero práctico" (The Practical Engineer) - Available in Brussels since 1696. Dedicated to Maximilian II Emanuel, Prince Elector of Bavaria

• "Elements of Euclid Amplified" - Published in Brussels, date unspecified.

• "Account of a country that has recently been discovered in North America, larger than Europe, and which is brought to light in Spanish by the Sergeant General of Battle..." - Published in Brussels, 1699. Dedicated to Juan de Dios de Silva y Mendoza y Haro, 10th Duke of the Infantado.

• "Brief Treatise on Geography divided into three parts: The first contains the Description of the River and Empire of the American Amazons, with its Geographical Chart: The second what the French and English possess, etc. in the New World, and how they introduce themselves there: And the third about the present state of the Empire of the Great Mughal and the Kingdom of Siam, and brought to light, under the protection of the Most Excellent Count of Fuensalida, by the Battle General Don Sebastian Fernandez de Medrano, Director of the Royal and Military Academy of the Army of the Low Countries." - Dedicated to the Count of Fuensalida and published in Brussels at the House of Lambert Marchant, Bookseller, 1700.

• "The first six books, eleven, and twelve, of the Geometric Elements of the famous philosopher Euclid of Megara" - Published in Antwerp, in 1686, dedicated to the Marquess of Bedmar. A reprint was published in Antwerp in 1728.

• "Brief Description of the World and Its Parts or Geographic and Hydrographic Guide, Divided into Three Books, Composed by Don Sebastian Fernandez de Medrano, Battle General, and Director of the Royal and Military Academy of the Army of the Low Countries" Published in Antwerp by Henrico y Cornelio Verdussen in 1709

• "Foundation and rules of the Academy called La Peregrina." - Publication details unspecified.

• "Infortunios de Alonso Ramirez" - also by Carlos de Sigüenza y Góngora, Pedro Vindel, and Louis Hennepin