Isabella I of Castile

Isabella I of Castile
April 22, 1451 – November 26, 1504

Isabella I of Castile was born on April 22, 1451, to King John II and Queen Isabella. In July 1454, the king died and was succeeded by Isabella’s older half-brother, Henry IV. The new king viewed his younger half-siblings as a threat to his power. As a result, Henry treated them poorly. Although sent away from court, the king later recalled his sister to keep an eye on her.

Meanwhile, Henry had more significant problems to deal with. The king was an incompetent ruler. During his reign, instability and lawlessness took hold in Castile. In turn, an alienated nobility began to support Henry’s younger half-brother, Alfonso. When Alfonso died in July 1468, the nobility shifted their support to Isabella.

In response to her new status, the princess sought to reconcile with her estranged brother. After negotiating, Henry and Isabella agreed to the Accord of Toros de Guisando in September 1468. Although Isabella became Henry’s heir, the king could choose his sister’s husband. Initially, Henry wanted Isabella to marry King Afonso V of Portugal. Instead, the princess sought to marry King John II of Aragon’s heir, Ferdinand. In October 1469, Isabella defied Henry and secretly married Ferdinand.

Queen of Castile

Ferdinand II of Aragon
Ferdinand II of Aragon

Upon learning of his sister’s betrayal, Henry IV declared that he’d no longer honor the Accord. Instead, the king chose his daughter, Joan, to be his new heir. As the king lay dying in 1474, he asked for Afonso V to marry Joan and become king. After Henry’s death, a war of succession erupted between Afonso and Isabella. Afonso invaded Castile and married Joan per Henry’s dying wish. However, in February 1479, Castile defeated the Portuguese, and Isabella I secured her throne.

In late 1479, John II died. Upon his death, Ferdinand II became king of Aragon. In turn, both rulers agreed to combine their kingdoms, creating a united Spain. Although the couple decided to rule equally, both domains remained politically independent. During their early joint reign, Isabella I and Ferdinand II focused on creating a Christian kingdom. As devout Catholics, they viewed it as their divine mission to expel the Muslims in Granada and convert Spanish Jews.


During the 8th century, the Muslim Umayyad Caliphate conquered the Iberian peninsula. After many centuries of fighting, Christians had reconquered all but Granada in southern Spain. In 1482, the king and queen began the Reconquista. For over a decade, the Spanish fought to defeat the Muslims. On January 2, 1492, Granada finally succumbed to Spanish forces. As the last Muslim stronghold fell, the monarchs now controlled a majority of the peninsula.

The Inquisition

In 1483, the queen and king created the Spanish Inquisition. The inquisition’s purpose was to punish heresy and to maintain strict adherence to Catholic doctrine. However, inquisitors were also tasked with converting Spanish Jews. As its leader, Isabella I appointed her confessor, Tomas de Torquemada. Under his leadership, heresy became treasonous, suspected Jews were tortured, and converted Jews were closely monitored.

Although a supporter of the Inquisition, Isabella I sought to temper some of the organizations more extreme practices. Inquisitors commonly used torture on suspected Jews and would burn them at the stake. Despite her concerns, Isabella still supported the Edict of Expulsion in 1492. The Edict demanded that Spanish Jews either convert or leave Spain. As a result, 20,000 Jewish families departed. In recognition of their efforts, Pope Alexander VI gave the “Catholic Monarchs” title to the royal couple.


In 1492, Isabella I agreed to finance Christopher Columbus’ expedition to the new world. The queen saw the trip as an opportunity to spread Christianity. When Columbus made contact with “Indians,” Isabella attempted to recognize them as citizens rather than slaves. At the same time, Columbus’ discovery brought new wealth and prestige to Spain. Despite this, the morality of slavery bothered the queen until her death.

Pope Alexander VI
Pope Alexander VI

Spain’s claim to the new world brought the country into conflict with Portugal. Pope Alexander VI had initially granted Isabella I and Ferdinand II all the newly discovered lands. However, the Portuguese king, John II, disputed Spain’s monopoly. To avoid conflict, Spain signed the Treaty of Tordesillas to end the dispute. The treaty would unknowingly allow Portugal to claim Brazil in the future.

Final Decade

During the last decade of her reign, Isabella I experienced multiple family tragedies. In 1497, her only son, John, died. In 1498, her eldest daughter, Isabella, died in childbirth. Two years later, the queen’s grandson, Miguel, also passed away. As a result of her eldest children’s deaths, the queen’s daughter, Joanna, became her heir. However, Joanna had begun showing signs of mental instability, which greatly concerned her mother.

In September 1504, Isabella I started suffering from a high fever and dropsy. By October, the queen could no longer rule on her own. After writing a long will, Isabella began repenting her sins. Finally, on November 26, 1504, the 53-year-old queen died. She had ruled Castile for 30 years and had been a joint ruler of Castile/Aragon for 25.


Isabella I overcame a Portuguese invasion to become the Queen of Castile. Through her marriage, Isabella joined her kingdom with Ferdinand II’s to create a united Spain. During her reign, the queen oversaw the Reconquista, the formation of the Spanish inquisition, and Spain’s rise as a European power. Although Isabella suffered personal tragedies, her children’s marriages would play an important role in Europe’s history. Joan’s son, Charles, would become Holy Roman Emperor, while Catherine would become the Queen of England.


Cavendish, R. (2004, November 11). Death of Isabella I of Castile. Retrieved November 28, 2020, from

Dougherty, M. J. (2018). Crusaders, Persecutors and Religious Reformers. In Kings & Queens of the Medieval World: From Conquerors and Exiles to Madmen and Saints (pp. 76-78). London: Amber Books.

Highfield, J. (2020, November 22). Isabella I. Retrieved November 28, 2020, from


Andy Tree

I'm a European history enthusiast who seeks to share his passion with others. I hope to inform and inspire readers with my posts!


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