Alfonso X of Castile

Alfonso X of Castile
November 23, 1221 – April 4, 1284

Alfonso X of Castile was born on November 23, 1221, in Burgos, Castile. At the age of 9, the prince’s father, King Ferdinand III, inherited the crown of Leon from his father, Alfonso IX. Since he already ruled Castile, Ferdinand combined both crowns to expand his kingdom, becoming the King of Castile and Leon. As a warrior ruler, Ferdinand fought against Muslims in the Iberian Peninsula during his reign. The teenage Alfonso assisted his father in his military campaigns and became a seasoned soldier. Through these efforts, Castile became a dominant kingdom in the peninsula.

As Alfonso grew, the prince became known as a scholar. In contrast to his warrior father, Alfonso developed an interest in writing and studying law. The prince’s time-fighting in Muslim territory exposed him to their culture, shaping his interest in learning. In turn, he preferred the company of scholars over military officers.  By the time Ferdinand died in 1252, the newly crowned Alfonso X had surrounded himself with scholars, writers, and poets.

King of Castile and Leon

At the Castilian court, Alfonso X promoted a culture of learning and encouraged new ideas. Jews, Muslims, and Christians were all welcomed by Alfonso, an unusual move at the time. The king became known for his writings and editing others’ works. With his scholars, Alfonso sought to reform Castile’s laws based on Roman law. To create a uniform legislature, the king began making the most comprehensive set of laws in Europe: the Siete Partidas (Seven-Part Code). The Siete Partidas would influence not only European law but North and South America’s legislative systems.

Alfonso X strongly promoted the use of the Castilian language. To this end, the king encouraged the translation of Arabic and Latin works into Castilian. During his reign, the court’s official language steadily changed from traditional Latin to Castilian. Through this policy, Alfonso streamlined documents, books, and Castile’s spoken language to create a more united kingdom.

Despite his preference for scholarly activities, Alfonso X didn’t shy away from war. In 1253, Castilian forces invaded Portugal and captured the Algarve. After overcoming King Afonso III, the two men made a peace agreement. After agreeing to marry Afonso’s daughter, Beatrice, the couple’s heirs would inherit the Algarve. Alfonso created an alliance with King Henry III of England against King Louis IX of France the following year. After the king’s daughter married Henry’s heir, Edward, Alfonso renounced his claim to the French duchy of Gascony.

Imperial Election

In 1257, Alfonso X of Castile was nominated as the next Holy Roman Emperor. Despite living far away from Germany, the king had a legitimate claim to the imperial throne. Through his mother, Alfonso descended from Emperor Frederick I. Although his election seemed unlikely, the king remained determined to become emperor. To further his ambition, Alfonso raised funds by debasing his coinage and imposing a tariff. The result of his unpopular economic policy ruined trade within the kingdom.

Alfonso X’s closest rival to the imperial throne was Henry III’s younger brother, Richard of Cornwall. Since it was doubtful he’d ever inherit the English throne, Richard aspired to gain his own crown. Unlike the Castilian king, Richard traveled to Germany and was crowned king. Over the next 15 years, Alfonso continued to press his claim. However, his campaign to become emperor proved unpopular amongst his nobility and the papacy. After Richard died in 1273, German princes elected Rudolf I of Habsburg instead of Alfonso, causing the king to finally renounce his claim.

Civil War

Having failed in his imperial aspirations, Alfonso X of Castile re-focused his attention on his kingdom. After his failed economic policy and imperial ambitions, the king had to contend with an unhappy nobility and his ambitious son, Sancho. In 1275, the king’s heir, Ferdinand, died at the Battle of Ecija. Although he left behind two young sons, Alfonso’s second son, Sancho, proclaimed himself his father’s heir. Despite the king’s preference for his grandsons, Sancho had the nobility’s support. After failing to resolve the issue peacefully, the succession dispute between Alfonso and Sancho turned into a civil war.

Sancho IV of Castile
Prince Sancho

By 1282, Alfonso X’s faction was losing the war. Eventually, Sancho overcame his father, securing his place in the line of succession. In turn, Alfonso lived out the last two years of his life effectively powerless. Due to their strained relationship, father and son would never reconcile. Shortly before his death on April 4, 1284, the bitter king left behind a will excluding Sancho from the succession. Despite Alfonso’s wishes, Sancho still became king after his father’s passing.


Although his later reign was overshadowed by civil war, Alfonso X’s earlier achievements can’t be overlooked. The king sparked an intellectual movement in his kingdom. Alfonso supported many scholars, writers, and poets who helped him with his reforms. Such reforms included creating a unified legislature and promoting the use of the Castilian language. Out of all his intellectual achievements, Alfonso’s Siete Partidas would have a lasting legacy not only in Europe but around the world.


Doubleday, S. R. (2015). The Wise King: A Christian Prince, Muslim Spain, and the Birth of the Renaissance. Basic Books.

Encyclopædia Britannica, inc. (n.d.). Alfonso X. Encyclopædia Britannica. Retrieved October 11, 2021, 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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