Treaty of the Bulls of Guisando

What it is

This treaty was agreed on 19 September 1468 at the Bulls of Guisando near Ávila, between King Henry IV of Castile and his half-sister Isabella. It followed years of civil war in Castile over the succession.

Why it matters

The treaty granted Isabella the title of Princess of Asturias, making her heiress presumptive to Castile, and removed Henry's daughter Joanna from the succession. This treaty became the legal foundation of Isabella's later claim to the throne, though Henry withdrew his support after Isabella married Ferdinand without his consent, leading eventually to renewed war. The modern plaque commemorating the site shows how this moment is remembered in Spain today.

Look closer

• Why might Henry IV have later gone back on this agreement?
• What does the treaty's unraveling tell us about the fragility of political promises between rival claimants?
• Why do you think this site was later marked with a commemorative plaque?