Afonso III of Portugal

Afonso III of Portugal
May 5, 1210 – February 16, 1279

Afonso III of Portugal was born on May 5, 1210, in Coimbra, Portugal. As the second son of King Afonso II and Queen Urraca of Castile, the prince wasn’t expected to inherit the throne. Seeking to create a life for himself, Prince Afonso emigrated to France. While abroad, Afonso married Countess Matilda II of Boulogne, becoming the Count of Boulogne. Although the prince spent several years in France, little else is recorded of his life outside Portugal.

In Portugal, King Afonso II began enacting reforms to centralize the monarchy’s authority. However, his reforms ignored an arrangement made by King Afonso I and the papacy. Instead of allowing the church to keep its many privileges, Afonso II sought to end them. In turn, the king came into conflict with Pope Honorius III. Despite threatening Afonso with excommunication, the king refused to back down. As a result, the pope excommunicated Afonso.

Afonso II agreed to reconcile with Honorius III to regain the papacy’s favor. However, the king died before making a serious effort. After Sancho II‘s accession, the new king inherited his father’s conflict with the church. A poor ruler, Sancho stubbornly chose to continue the monarchy’s feud with the papacy. Lacking support from his citizens, the king unwisely made two powerful enemies that actively sought his downfall.

King of Portugal

Sancho II of Portugal
Sancho II of Portugal

In 1246, Pope Innocent IV issued a papal bull declaring Sancho II’s throne forfeit. In turn, the Portuguese had the pope’s blessing in choosing their new king. Deciding on the king’s younger brother, Prince Afonso was offered the throne. With the pope’s backing, Afonso returned to Portugal and engaged in a brief civil war with Sancho. By 1247, the prince emerged victoriously, and his brother fled into exile.

Ascending the throne as King Afonso III of Portugal, he immediately began restoring the monarchy’s prestige. Capitalizing on his newfound popularity, Afonso held a Cortes, or general assembly, of representatives from Portugal’s social classes in 1254. Learning from Sancho’s mistakes, the king made an effort to listen to his subjects. Unlike his brother, Afonso proved to be a capable and active administrator. The king advocated for equal representation for all throughout his reign, reformed the justice system, and improved taxation.

Although Afonso III enjoyed a good relationship with his subjects, the same couldn’t be said about his wife. After 15 years of marriage, Matilda hadn’t given Afonso any heirs. Frustrated, the king claimed his wife was barren and sought a divorce. The relationship between the royal couple got so bad that Afonso refused to let Matilda join him in Portugal. The king ultimately got his way, and the couple divorced in 1253. Afonso later remarried King Alfonso X of Castile’s illegitimate daughter, Beatrice, the same year.

 Foreign Policy

Having achieved domestic peace, Afonso III focused on expanding Portugal’s borders. To this end, the king launched a military campaign against the Moors (Muslims) in the south. The king sought to complete the conquest of the Algarve. After invading the kingdom, the royal army captured the capital of Faro, securing the Algarve for Portugal. In turn, Afonso’s kingdom now extended along the entire western coast of the Iberian Peninsula.

Regarding the church, Afonso III had a strained relationship with the papacy. Although the king had learned much from his brother’s mistakes, he still felt the need to tax the church. Afonso sought to decrease the church’s power by taking some of its enormous wealth. However, the papacy refused to consent to the king’s demand. Like his father and brother, the pope excommunicated Afonso for challenging the church’s power in Portugal.

Final Years

During the last several years of Afonso III’s reign, the aging king came into a border dispute with Castile. Castile believed the Algarve to be their rightful territory, not Portugal’s. The king disagreed, and Portugal engaged in a war with Castile. Finally, in 1267, peace was reached. Portugal and Castile agreed that the southern border between the two kingdoms would be the River Guadiana. The border remains over 750 years later.


On February 16, 1279, Afonso III of Portugal died from natural causes. On his deathbed, the king submitted himself to the pope. Afonso left behind a rich legacy of progressive reforms and military success. The king stabilized his kingdom by promoting equal representation, improving the justice system, and fair taxation. His reign saw the completion of the conquest of the Algarve, expanding Portugal’s border further south. After his death, Prince Denis succeeded his father.


Disney, A. R. (2009). A History of Portugal and the Portuguese Empire: From Beginnings to 1807 (Vol. 1). New York City, NY: Cambridge University Press.

Encyclopædia Britannica, inc. (n.d.). Afonso III. Encyclopædia Britannica. Retrieved February 3, 2022, 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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