A Portuguese army under John of Aviz and Nuno Álvares Pereira destroyed a much larger Castilian invasion in 1385, securing Portugal's independence and the House of Aviz.
The Battle of Aljubarrota was fought on 14 August 1385 between the Kingdom of Portugal, led by the newly acclaimed John I and his constable Nuno Álvares Pereira, and a much larger invading army of the Kingdom of Castile under John I of Castile. It was the decisive engagement of the 1383–1385 Interregnum, the succession crisis that followed the death of Ferdinand I.
The outnumbered Portuguese won a crushing victory using a prepared defensive position, dismounted men-at-arms, and English longbowmen. The result secured Portuguese independence from Castile and confirmed the House of Aviz on the throne, shaping the kingdom that would soon launch the Age of Discovery.
Ferdinand I, the last king of the House of Burgundy, died in 1383 leaving only a daughter, Beatrice, married to John I of Castile. The prospect that Portugal would be absorbed into the Castilian crown provoked widespread resistance, and the regency of the queen mother Leonor Teles was distrusted.
John of Aviz, an illegitimate son of Peter I and Master of the Order of Aviz, led the opposition, and in 1385 the Cortes of Coimbra acclaimed him King John I. John I of Castile invaded Portugal to enforce his own claim, and the two armies met near the village of Aljubarrota.
The Portuguese army was significantly smaller but well positioned and disciplined, commanded in the field by the constable Nuno Álvares Pereira, one of the ablest generals of the age, while the king held the reserve. It included a contingent of English longbowmen, reflecting the growing Anglo-Portuguese partnership.
The Castilian army was larger and included French allied men-at-arms and crossbowmen. Its size gave it confidence, but the narrow, prepared battlefield chosen by the Portuguese neutralised that advantage.
The Portuguese occupied a hill with their flanks protected, men-at-arms dismounted in the centre and archers on the wings, and dug ditches and pits to break up a mounted charge. The Castilian vanguard, attacking uphill into a constricted front, was shot down and driven back onto the advancing main body.
As the main Castilian host pressed forward it lost cohesion in the same killing ground, exposed to the longbowmen and unable to bring its numbers to bear. The Portuguese line under Nuno Álvares held and then counterattacked, turning the Castilian confusion into a rout.
The Castilian army was destroyed and John I of Castile fled the field. Portuguese independence was secured, and John I's throne and the House of Aviz were confirmed beyond challenge.
In thanksgiving John I founded the Monastery of Batalha — literally "Battle" — one of the masterpieces of Portuguese Gothic architecture, and in 1386 he sealed the Treaty of Windsor with England, the oldest active alliance in the world.
Aljubarrota is the founding military event of the House of Aviz and one of the decisive battles of Portuguese history: it preserved the kingdom's independence at the moment it was most in danger of Castilian absorption.
It also demonstrated, like the contemporary battles of the Hundred Years' War, the power of a prepared defensive position combining dismounted men-at-arms and massed archery against a larger force of mounted and heavy troops.