The Battle of Aljubarrota was fought between the Kingdom of Portugal and the Crown of Castile on 14 August 1385. Forces commanded by King John I of Portugal and his Constable Nuno Álvares Pereira, with the support of English allies, opposed the army of King John I of Castile with its Aragonese and French allies, as well as Genoese mercenaries at São Jorge, between the towns of Leiria and Alcobaça, in central Portugal. The result was a decisive victory for the Portuguese, ruling out Castilian ambitions to the Portuguese throne, ending the 1383–85 Crisis and assuring John's position as King of Portugal.
Portuguese independence was safeguarded and a new dynasty, the House of Aviz, was established. Scattered border confrontations with Castilian troops would persist until the death of John I of Castile in 1390, but these posed no real threat to the new dynasty.