Treaty of Tagilde

This agreement is considered to have constituted the first legal foundation of the Anglo-Portuguese Alliance, which continues to exist.

Prior to the treaty, there had been disputes over the Castilian throne between D. Pedro and his illegitimate brother, D. Enrique de Trastámara.

For Ferdinand, the treaty provided an opportunity to assert the independence of Portugal against interference from Castile.

The treaty agreed that the two signatories would wage war against Castile on two fronts: the English on the north and the Portuguese to the west.

In 1385, the Portuguese army, with help from English soldiers, defeated Castilian forces at the Battle of Aljubarrota.