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Primary sourceDocument4 September 1479

Treaty of Alcáçovas

4 September 1479

The 1479 peace treaty ending the War of the Castilian Succession, confirming Isabella as queen of Castile and dividing Atlantic territories with Portugal.

This treaty confirmed Isabella's claim to the throne of Castile and shaped Spain's later overseas ambitions.

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Black and white scan of a handwritten 15th-century Spanish manuscript page. Faded notes at the top include the date 'marzo 1480' and a seal impression sits in the upper middle. A label reads 'RGS III-1480 302' and a stamp reads 'Archivo General de Simancas'. Dense cursive handwriting fills the page below a large initial letter.
Treaty of Alcáçovas, notification copy, 1480. Archivo General de Simancas.

About this source

What it is

This is a 15th-century Spanish manuscript recording the Treaty of Alcáçovas, signed on 4 September 1479 between the Catholic Monarchs of Castile and Aragon and King Afonso V of Portugal and his son. It is held in the Archivo General de Simancas.

Why it matters

The treaty ended the War of the Castilian Succession, in which Portugal had backed Isabella's rival Joanna la Beltraneja for the throne. It confirmed Isabella as queen of Castile while giving Portugal control of most Atlantic territories and exploration rights, a division that later shaped the Treaty of Tordesillas. It shows how dynastic disputes and overseas exploration were tightly linked in this period.

Look closer

  • Why did settling the succession in Castile also require dividing up unexplored Atlantic territory?
  • What does the treaty's treatment of Joanna la Beltraneja reveal about how royal women's claims were handled?
  • What do the marriage arrangements in the treaty tell us about how peace was secured between rival crowns?

This document is part of the curated material that grounds the AI version of Queen Isabella I on Humy.ai — when students ask about related events, the AI can quote it and cite it.

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