The House of Avis

When Fernando died in 1383, he left no male heir to the throne. His only daughter, Beatriz, was married to Juan I, king of Castile. The marriage writ stipulated that their offspring would inherit the Portuguese crown if Fernando left no male heir and that, until any children were born, Portugal would be ruled by a regency of Fernando's widow, Leonor Teles. When Fernando died, Leonor assumed the regency in accordance with the marriage writ. The assumption of the regency by the queen was badly received in many Portuguese cities because Leonor was a Castilian and considered an interloper who intended to usurp the Portuguese crown for Castile and end Portugal's independence. Leonor's principal rival for control of the throne was João, the master of the Order of Avis and illegitimate son of Fernando's father, Pedro I (r.1357-67). On December 6, 1383, João broke into the royal palace and murdered Count Andeiro, a Galician who had been Fernando's chancellor. Leonor Teles fled to the town of Alenquer, the property of the queens of Portugal. She appealed to Juan I for help, and he invaded Portugal in January 1384. Leonor abdicated as regent. In Lisbon the people proclaimed João to be the governor and defender of the realm. João immediately began to prepare an army and sent a mission to England to recruit soldiers for his cause.

Wars with Castile

The bourgeoisie of Lisbon, enriched by commerce, decided to support João and donated substantial sums for war expenses. Money also arrived from the bourgeoisie in Porto, Coimbra, and Évora. The majority of the nobility, among whom national sentiment was not well developed and feudal customs based on oaths of vassalage were still obeyed, took the side of Juan of Castile, which gave him the support of fifty castles. A few nobles, however, including Álvaro Pais, João Afonso, and Nun'Álvares Pereira, were more attuned to national sentiment and sided with João.

In March 1384, Juan marched on Lisbon, which he besieged by land and sea. In April, in the Alentejo, Nun'Álvares Pereira defeated the Castilians at the Battle of Atoleiros, a victory that resulted from the new military tactic of forming defensive squares from dismounted cavalry because the Portuguese had far fewer troops than the enemy. The siege of Lisbon was broken after seven months by an outbreak of the plague in the Castilian camp, and Juan retreated to Seville to prepare another invasion the following year.

The retreat of the Castilians gave João an opportunity to legitimate his claim to the throne. In March 1385, a cortes was summoned to resolve the succession. João's case was argued by João das Regras, who attacked the claims of the various pretenders to the throne. On April 6, the opposition ended and João was proclaimed king as João I (r. 1385-1433). The new king named Nun'Álvares Pereira constable of Portugal. At the same time, a contingent of English longbowmen began to arrive. Nun'Álvares Pereira marched north in order to obtain the submission of Braga, Guimarães, and other places loyal to Juan, who responded by sending an army to attack Viseu. The Portuguese routed this Castilian force at Rancoso using the same new military tactic that brought them victory at Atoleiros. Juan, nonetheless, was still intent on besieging Lisbon and led his army southward. João I and Nun'Álvares Pereira decided to engage Juan's army before it arrived in the capital. The two armies met on the plain of Aljubarrota about sixty kilometers north of Lisbon on August 14, 1385. Using the same tactic of defensive squares of dismounted cavalry that had brought them success in previous battles, a force of 7,000 Portuguese annihilated and scattered a Castilian army of 32,000 in little more than thirty minutes of combat. Although additional battles were fought and final peace was not made with Castile until October 1411, the Battle of Aljubarrota secured the independence of Portugal for almost two centuries.