A disputed succession divides the nobility
King Fernando I of Portugal died in October 1383. His legitimate heir Beatriz had married Juan I of Castile, entwining succession with relations between the kingdoms and the distribution of court power. João, master of the Order of Avis, led another faction and was chosen king by the Cortes at Coimbra in 1385, becoming João I.
Some Portuguese nobles supported Beatriz and Juan, while others joined João and Pereira. Great-family interests, competing branches and lord–vassal relations shaped choices. João’s side included English and Gascon auxiliaries; French fighters joined the Castilians, connecting the dynastic war with Anglo-French rivalry.
References: [2]
Circling and changing direction
Juan’s army advanced toward Lisbon while Portuguese forces sought to intercept it north of the capital. On 14 August 1385, a Monday in the contemporary Julian calendar, João’s troops took positions on the São Jorge heights near Aljubarrota. They faced north in the morning, with watercourses and slopes complicating a frontal assault. The Castilians circled toward gentler ground instead of attacking directly.
The Portuguese moved about two kilometers south and redeployed where the heights narrowed. Juan’s subsequent letter to Murcia describes the detour, exhaustion and disagreements: experienced knights advised postponing battle while other forces had already attacked. He also described his illness and prolonged use of a litter, assigning part of the defeat to a hasty assault.
A narrow front and two lines
The second position combined natural terrain with ditches, pits and felled trees that restricted the enemy’s deployment. Juan’s letter specifically mentions waist-high tree obstacles, deep ditches and a narrow front between stream valleys. The ground compressed the approach and prolonged exposure to arrows and crossbow bolts.
Pereira led the front line, with archers and crossbowmen on the flanks, while João commanded reserves in a line behind; the baggage was separately protected. Monteiro’s analysis of accounts and terrain questions the conventional depiction as a closed, regular “Nuno square.” Cooperation among dismounted armored men, infantry and shooters resembled methods used earlier by English armies, with effectiveness depending on local terrain and mutual support.
Why greater numbers did not decide the encounter
The Castilian army was larger. Monteiro argues that part of its long marching column had not yet arrived, while valleys and narrow access restricted the flanks of those present. The number able to join close combat was therefore limited, preventing full use of the potential numerical advantage.
Battle began toward evening. Shooters struck the approaching troops before close foot combat, after which the Portuguese rear line advanced in support and the flanks helped press the attackers. Chronicles differ over whether the first assault was mounted or dismounted and how successive attacks connected. The Castilian force quickly lost organization; Juan withdrew to Santarém and then traveled by water to his fleet. The main clash was brief, but flight, pursuit and killing continued beyond the battlefield.
Comparing human remains with written accounts
Excavations beginning in 1958 found ditches, pits and collective burials. Later research considered terrain defenses alongside combat injuries. A study published in 2001 analyzed 2,874 bone specimens representing an estimated minimum of 414 people. Cuts, punctures and metal residues provided physical evidence of the fighting.
The remains also preserved healed injuries and disease, allowing researchers to distinguish older damage from trauma around death. Terrain surveys, chronicles and skeletal analysis record defensive positions, encounters and injuries from different perspectives that can be compared.
References: [3]
A stronger dynasty while war continued
Victory stopped this Castilian advance and strengthened João I and the Avis dynasty. Court power and estates were redistributed, with Pereira and other supporters gaining prominence. Monteiro relates that outcome to interests and allegiance within noble factions.
Juan still styled himself king of Portugal in his letter of 29 August, asking Murcia to send representatives to a planned October assembly to prepare further action. Royal claims and subsequent warfare continued after the military defeat.