The Treaty of Alcáçovas was signed on 4 September 1479 between the Catholic Monarchs of Castile and Aragon on one side and Afonso V and his son, Prince John of Portugal, on the other side.
It put an end to the War of the Castilian Succession, which ended with a victory of the Castilians on land and a Portuguese victory on the sea.
The four peace treaties signed at Alcáçovas reflected that outcome: Isabella was recognized as Queen of Castile while Portugal reached hegemony in the Atlantic Ocean.
Treaty of Alcaçovas. Notification of the treaty to the city of Seville, March 14, 1480. 1st page.
Ferdinand and Isabella
Afonso V of Portugal
Catholic Monarchs of Spain
The Catholic Monarchs were Queen Isabella I of Castile and King Ferdinand II of Aragon, whose marriage and joint rule marked the de facto unification of Spain. They were both from the House of Trastámara and were second cousins, being both descended from John I of Castile; to remove the obstacle that this consanguinity would otherwise have posed to their marriage under canon law, they were given a papal dispensation by Sixtus IV. They married on October 19, 1469, in the city of Valladolid; Isabella was 18 years old and Ferdinand a year younger. It is generally accepted by most scholars that the unification of Spain can essentially be traced back to the marriage of Ferdinand and Isabella. Their reign was called by W.H. Prescott "the most glorious epoch in the annals of Spain".
Wedding portrait of Queen Isabella I of Castile (right) and King Ferdinand II of Aragon (left), married in 1469
Ferdinand and Isabella with their subjects
Crowns and Kingdoms of the Catholic Monarchs in Europe (c. 1500)
Virgin of the Catholic Monarchs (c. 1491–93). The Virgin Mary (center), with St Thomas Aquinas symbolically holding the Catholic Church and St Domingo de Guzmán, Spanish founder of the Dominican Order, with a book and a palm frond. Ferdinand is with the prince of Asturias and the inquisitor; Isabella with their daughter, Isabel de Aragón.