How a small Portuguese force crushed a massive invasion to secure national independence
On 14 August 1385, the Kingdom of Portugal faced a massive Castilian invasion. Despite being outnumbered, the Portuguese army utilized innovative defensive tactics and field fortifications to secure a decisive victory. This triumph ended a two-year succession crisis, established the House of Aviz, and permanently safeguarded Portuguese sovereignty.
The 1383–85 crisis began when King Ferdinand I died without a male heir, leaving the throne contested. Princess Beatrice, married to King John I of Castile, held a claim that threatened to absorb Portugal into Castile. Amidst this instability, John of Aviz, the illegitimate son of Peter I, emerged as the champion of Portuguese independence. Supported by Lisbon merchants and the military commander Nuno Álvares Pereira, John of Aviz was acclaimed king in April 1385, prompting a full-scale Castilian invasion.
The decisive clash occurred near Leiria at São Jorge. Álvares Pereira, a master of defensive warfare, positioned his troops on a hill protected by natural obstacles and a sophisticated network of trenches and caltrops. Drawing on tactical lessons from the Hundred Years' War, the Portuguese combined archers with dismounted men-at-arms. When the Castilian army, numbering 31,000, attempted to maneuver around the position, the Portuguese quickly redeployed to maintain their tactical advantage. The battle lasted only about an hour, ending in a rout of the Castilian forces.
The victory was total, resulting in the death or capture of significant Castilian nobility and the collapse of their military ambitions. To commemorate this divine favor, King John I commissioned a grand monastery at the site. The battle not only solidified the House of Aviz but also cemented a lasting military alliance with England, formalized by the 1386 Treaty of Windsor. The site remains a protected national monument, with archaeological excavations revealing the extensive defensive systems that allowed a smaller force to overcome a superior adversary.
Source: Battle of Aljubarrota
