Ferdinand and Isabella: The Marriage That Unified Spain

The Kingdom of Spain charts its origin in the marriage of Ferdinand and Isabella in 1469. Their union, and their rule, triggered a war that forged the modern world.

May 31, 2022By Charles J. Lockett, MA in Politics, BA in History and Politics
isabella and ferdinand portraits


The marriage of Ferdinand II of Aragon and Isabella I of Castile is one of the most masterful pieces of political theater in history. It was far from a love-story — while, by all accounts, Ferdinand and Isabella were a cordial and possibly even happy couple, their union was the accumulation of hundreds of years of Spanish history, forged by war and intrigue into a dynastic union that laid the foundations for the modern Spanish state. This is the tale of the Catholic monarchs of Spain.


Ferdinand and Isabella: Written in the Stars

spain kingdoms before ferdinand and isabella
Map of Spain in 1360, via the University of Texas, Austin


The scene was set for Ferdinand and Isabella’s union of Aragon and Castile some time before their births. Aragonese elites had grown tired of being vassals to Catalan interests, and their chance arrived in 1410, with the death of the pleasingly-titled Martin the Humane in 1410. His death without heirs ended the House of Barcelona, and Aragonese powerbrokers managed to place a Castilian prince, Ferdinand of Antequera, on the throne of Aragon — with behind-the-scenes support of the expansionist Castilians. This event permanently entangled the two states, and meant that they only required a formal intermingling of claims to create a full dynastic union. However, every plan has its discontents.


The Headstrong Infanta

isabella portrait
Portrait of Queen Isabella, circa 1470-1520, via the Royal Collections Trust


Isabella was born in 1451, into a world in which women fought for every shred of political power. But from an early age, Isabella was viewed by her father John II of Castile as a means of expanding Castilian territory in pursuit of the elusive goal of uniting Spain. She was first betrothed to an Aragonese prince at age six — her future husband Ferdinand — but other considerations intervened. This agreement was broken by her promise to a Portuguese king and a Castilian civil war forced her betrothal to a member of the Castilian court. However, when naming the 17-year-old Isabella as his heir, her uncle King Henry IV of Castile agreed never to force her to marry and to obtain her consent for any match. Isabella, now able to plot her own destiny, returned to the idea of marriage with Ferdinand of Aragon.


The Boy Warrior

ferdinand portrait contemporary
Portrait of King Ferdinand V, c 1470-1520, via the Royal Collections Trust


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For his part, Ferdinand was similarly brought up in a conflict-ridden court, though his early life was characterized both by dynastic conflict between his father and his elder brother, and by peasant revolts against their feudal overlords. Ferdinand’s unpopular father was widely opposed by the nobles, who supported Ferdinand’s brother when he rose up in rebellion against his father in the Catalan Civil War. Ferdinand, however, stayed loyal. This had two effects on Ferdinand: firstly, it gave him significant military experience as one of his father’s lieutenants, and he became an experienced leader even before his 18th birthday. Secondly, the suspicious death of his brother in the custody of his father left him alone as heir to the throne of Aragon. Although his contemporary portraits are somewhat less than impressive to our modern eyes, accounts are of a warm, engaging and attractive young man, who wielded a prodigious intellect.


A Conscious Choice

henry iv castile
Henry IV of Castile, by Francisco Sainz, 19th century, via the Museo del Prado


This was not a love-match; the two had never even met — it was a highly choreographed political union — but without a doubt both Ferdinand and Isabella actively chose their marriage as a conscious political course of action. Ferdinand and Isabella met but a few days before their marriage in mid-October 1469. The meeting of the two heirs took place against the wishes of King Henry IV of Castile, who now saw Isabella as an inconvenient and headstrong threat to his own plans. Although Henry had agreed to permit her to marry as she wished, Isabella feared that she would be done away with, and so she escaped from court on the pretext of visiting her family graves. Meanwhile, Ferdinand traveled through Castile disguised as a servant! In a relatively small ceremony, Ferdinand and Isabella were married on 19th October 1469.


There was, however, a delicate issue to be navigated. The complex interwoven nature of Spanish dynastic politics meant that Ferdinand and Isabella were second cousins; they shared a great-grandfather in King John I of Castile (1358 -1390). This meant that they fell under the status of consanguinity — being too closely related for the Catholic Church to sanction their marriage. Such taboos were well-established by the Catholic Church in propaganda and in practise. But, while their blood relationship would have proven an irreconcilable obstacle for non-nobles (or even nobles without the right connections), a Papal dispensation was attained. The precise nature of this dispensation is somewhat murky — it was signed by Pope Pius II, but he had died five years previously in 1464. It seems likely that, given the urgency of his requirements for political alliances, John II of Aragon and powerful Churchman Rodrigo de Borja (future Pope Alexander VI) forged the document.


Political Considerations

joanna beltraneja ferdinand and isabella
Joanna “la Beltraneja”, by Antonio de Holanda, c. 1530, via Wikimedia Commons


While the stage was set for the union of the two crowns, the marriage between Ferdinand and Isabella was also an immediate consideration for the ongoing Catalan Civil War. As part of the marriage, a treaty was signed between Ferdinand and Isabella: Castile would become formally superior over Aragon. Isabella would rule over all of Castile and Aragon as Queen, with Ferdinand as her consort, in return for its aid in the Civil War. For this reason, it was known as the “Capitulations of Cervera”.


The document was even read out during the marriage proceedings — underlining the fact that this was a highly political arrangement. As well, this was not a deal done between Castile and Aragon per se: although it had the covert support of Ferdinand’s father John II of Aragon, Isabella’s uncle Henry IV of Castile was entirely cut out of the process. This shows that Isabella was seeking to create her own independent political power, very much against that of her uncle and his heirs. Upon learning of Isabella’s actions shackling him into a civil war, her uncle King Henry was furious, disinheriting her in favor of his own daughter Joanna. Sadly, Joanna was the subject of much mockery due to her association with the unpopular King, and she was rumored to be the illegitimate daughter of the Queen’s favorite Beltrán de la Cueva — hence she was known by the unkind moniker la Beltraneja; “the one who looks like Beltrán”.


Made Queen by Force of Will

map of spain regions
Map of Spain’s Regions, via Nationsonline.org


However, Isabella was not going to take disinheritance lying down. Upon Henry’s death in 1474, Joanna was Henry’s named successor — but, as Isabella demonstrated throughout her life, shrewd politics and the precise application of force beat ancient right every time. Racing to Segovia, she convened the noble court and, largely by force of will, declared herself Queen of Castile — with Ferdinand as her “legitimate husband”. Isabella was determined to follow the trend toward powerful women in European Renaissance society.


Though beaten to the first punch, Joanna’s supporters began to regroup and plan a rebellion in concert with a Portuguese invasion, which would become the War of the Castillian Succession. Hastening to Segovia, Ferdinand was welcomed into the city as a king. Yet this did not mean that Ferdinand and Isabella could simply forget all other considerations and rule jointly as Catholic monarchs: each stood at the head of an enormously complex set of obligations and political interests, which frequently opposed one another. Upon Isabella’s accession to the throne, they signed the Concorde of Segovia, which named Ferdinand King of Castile alongside Queen Isabella — but reserved the exclusive right for Isabella’s heirs to inherit Castile, and gave her a sort of regal veto if they could not agree. This represented months of legal and political wrangling between the two camps.


Forged in the Fires of War

battle toro ferdinand and isabella
Battle of Toro, by Francisco de Paula van Halen, c. 1850, via the National Library of Portugal


Within a matter of months of her seizure of the throne, the supporters of Joanna la Beltraneja had risen against Isabella, and King Afonso of Portugal saw the opportunity to bring Castile under his control. Scandalously, Afonso took Joanna, his own neice, for his wife, and supported the rebellion with an invasion from the west. Unsurprisingly, foreign intervention into wars over Spanish succession are not an infrequent historical occurrence.


The War of the Castilian Succession, as this conflict is known, was ironically the making of Ferdinand and Isabella. Afonso and Joanna’s Juanistas were militarily ineffective, and although the Castilian-Aragonese Isabellista army that fought them made little headway, Ferdinand and Isabella portrayed the stalemate as a stunning victory. They launched a highly successful propaganda campaign throughout Spain that painted them as a new force in Spanish politics. As well, the war drove the two kingdoms of Castile and Aragon closer together, and Isabella formally granted her husband all of her regal power as co-regent in 1475.


At the same time, Ferdinand’s military skill prevented the French from creating a foothold in Narvarre, and so by the end of 1476, la Beltraneja’s alliance was disintegrating, with Isabella secure on the throne. Isabella showed significant political acumen with a carrot-and-stick approach, offering exculpations to nobles who would renounce Joanna, while dealing brutally with those that continued to resist. In February of 1479, Ferdinand’s father John II of Aragon passed away, and a far more orderly transition of power took place, with Ferdinand’s coronation as King of Aragon.


Ferdinand and Isabella: The Casualties of Peace

columbus visits ferdinand and isabella
Christopher Columbus At The Court Of The Catholic Monarchs, by Juan Cordero, 1850, via Google Arts and Culture


Afonso failed to raise any further interest from Louis XI of France in continuing the war, and in 1479 he suffered a blow by the Pope, who reversed the dispensation given for his marriage to his niece. In September of that year, lacking legitimacy, French allies, and Castilian dissenters, Afonso called it quits and signed the Treaty of Alcáçovas, in which he and the Catholic monarchs renounced all of their claims to each other’s kingdoms. The treaty also set up broad spheres of influence for future expansion, and was sealed by Ferdinand and Isabella’s daughter’s marriage to Afonso’s son (along with a hefty dowry of 106,000 gold doubloons). La Beltraneja was sent off to a monastery, and took little further part in Castilian politics — a casualty of peace.


By 1480, the joint rule of Ferdinand and Isabella over a united Spain was an established fact. Ferdinand, through his father, became King of Aragon and Sicily, and Count of Barcelona. Isabella, through right of conquest from la Beltraneja and the Portuguese, was Queen of Castile and Leon. The Concorde of Segovia (later expanded by Isabella’s war measures) conferred the co-regency of all of her lands upon Ferdinand, and in 1481, Ferdinand granted all of the same rights to Isabella. The Catholic monarchs combined their arms, into a single escutcheon featuring the arms of Castile, Leon, and Aragon. Thus, in all ways, their rule marked the end of the Spanish Kingdoms and the beginning of the Kingdom of Spain.

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By Charles J. LockettMA in Politics, BA in History and PoliticsEver since Charles was a lad, he’s been a history obsessive – he spent his summer holidays dragging his family around Welsh castles! He pursued that passion through University, studying Early-Modern Europe and the French Revolutions, receiving his MA in Politics from the University of Sheffield. Nowadays, he is a historical writer and researcher specializing in Medieval and Early Modern history, based in Yorkshire, UK. In his spare time, he is a Dungeon Master, aspiring fantasy novelist and cat dad.