The choice of the cortes notwithstanding, in the spring of 1385 João I’s throne was far from secure. The legitimists remained strong in the north, and Juan was preparing a new invasion; João knew he must fight, and he desperately needed allies. With this in mind, even before his election he had sent emissaries to England to seek recruits and urge Gaunt once again to revive his claim to the crown of Castile. With difficulty, his agents engaged a small Anglo-Gascon force which reached Portugal while the cortes was still in session. Once proclaimed, João moved quickly to secure a formal alliance with Richard II, and the outcome was the treaty of Windsor signed in May 1386. Under the terms of this treaty each king agreed to provide the other with military and naval assistance on request and to grant reciprocal trading rights to their respective citizens in each other’s territory. Richard also promised to support João against any enemy who tried to overthrow him, and João sent Richard a squadron of galleys. The treaty of Windsor was the foundation stone of the long-lasting Anglo-Portuguese alliance.
Nuno Álvares Pereira meanwhile had been appointed constable of the king’s army, and in 1385 both he and João campaigned in the north where they took a string of legitimist towns, including Braga. Early in July a large Castilian raiding party was defeated at Trancoso in Beira Alta; then a few weeks later Juan crossed the border with the main Castilian army. Juan, whose force numbered perhaps 20,000 men including many legitimist Portuguese and a contingent of French men-at-arms sent by Charles VI, planned to crush the patriots with overwhelming force. He advanced towards Lisbon along the well-worn invasion route down the Mondego valley. João, on Nuno Álvares’s advice, decided not to retreat behind the walls of his capital, but to stand and fight. On 14 August 1385 João’s army of about 7,000, including the small contingent of men-at-arms and archers recruited in England, occupied defensive positions on a ridge called Aljubarrota, overlooking the Leiria-Lisbon road. The van was commanded by the constable, the main body by the king. A division of Portuguese knights and bowmen was on the right flank and the Anglo-Gascons on the left.
This was a battle between João of Portugal and Juan I of Castile, rival claimants to the Portuguese throne. The Castilian army comprised 6,000 men-at-arms (including 800 or 1,500 French mercenaries under Geoffroi de Parthenay), 2,000 jinetes, 10,000 infantry (archers, spearmen and dart-throwers) and 16 light cannon (which fired off only a few inconsequential rounds during the action). João’s forces were somewhat smaller, though numbering at least 7,000 including 2-3,000 men-at-arms; Ayala says there were 2,200 men-at-arms and 10,000 others, Froissart giving 2,500 men-at-arms and 12,000 infantry. The infantry included many archers, mostly Portuguese but including some English longbowmen (commanded by 3 esquires according to Froissart); the English element probably numbered about 700 and certainly not less than 400, Froissart saying that there were about 500, one-third of them companions.
After several hours of jockeying for position the Portuguese were formed up amidst orchards half-way down a slope by the abbey of Aljubarrota; they had felled brushwood waist-high to cover both flanks, behind which were drawn up their archers and crossbowmen (with the English on the left wing), with men-at-arms formed up on foot in the centre in a hollow square behind the single narrow passage through the archers’ barricades. They also dug a trench to their front, with two further shallow ditches containing streams providing additional protection for the flanks.
Juan, inadvisably forced to take action by young Castilian hotbloods, resolved to advance against this strong Portuguese position, despite the fact that his army had been marching for several hours and it was already late afternoon. He advanced in 3 lines, the first of his French mercenaries, the second of the Castilian horse in 3 divisions, and the third of the crossbowmen and other infantry.
Coming upon Joao’s positions, the French dismounted and began their attack without awaiting the arrival of the rest of the Castilian army. Heading for the gap between the abattis on the Portuguese flanks they were enfiladed by archers and javelinmen and despite making an initial impression in the Portuguese line they were soon repulsed by Joao’s men-at-arms, losing hundreds killed and 1,000 captured, these being subsequently killed by the Portuguese, who became concerned at having so many prisoners in their rear. Juan, failing to realise the magnitude of his van’s defeat, then launched a cavalry charge against the Portuguese, whom he was unable to outflank because of the nature of the battleground, which channelled his entire force directly at their dismounted men-at-arms so that the Portuguese infantry could enfilade them just as they had the French. The ditch presented a serious obstacle, allegedly only becoming passable when, in 40 places, it had become filled with the carcasses of shot-down horses, and reputedly not a single Castilian of some 500 who crossed over it came back alive.
When after less than an hour’s confused fighting Juan’s standard-bearer fell the exhausted Castilians began to falter, to break in rout soon after following Juan’s own flight from the battlefield. They had lost 7,500 men including 2,500 men-at-arms according to João’s own account, among them the Masters of Calatrava and Santiago, both Castilian marshals, de Parthenay and many other leading noblemen. Predictably, Portuguese losses appear to have been minimal.
Fighting in the van, many of the Portuguese legitimist leaders were mowed down – an outcome with major long-term political consequences. The rest of the invading host simply disintegrated; Juan himself was forced to flee, his campaign ending in ignominious failure. Aljubarrota proved one of the most consequential victories in Portuguese history. It confirmed the rule of João I and the house of Avis, demonstrated Portugal’s emphatic rejection of the idea of Iberian union and constituted a defining moment in the evolution of national consciousness.
Afterwards, near the place where the battle had been won, and in fulfilment of his vow on the day it was fought, João ordered an abbey be raised. Builders worked on its construction for almost 150 years, and even then it was never completed. Nevertheless, the unfinished monument – which was called Batalha (battle) abbey – is unquestionably a magnificent example of late Gothic architecture and one of the few truly outstanding buildings ever created in Portugal. It was and is a fitting symbol of the new dynasty and the triumphant reassertion of the kingdom’s independence.
A major battle involving the use of black powder weapons was at Aljubarrota on 14 August 1385, fought between the Portuguese and the army of the Spanish kingdom of Castile. The Portuguese had inferior numbers and took defensive positions behind a trench and brushwork palisades in order to keep the Castilian cavalry from making a charge. As an added measure they dug a chequered pattern of holes in the field in front in order to trip up their opponents’ horses. Creeks and steep terrain protected their flanks. The Castilians, seeing a direct assault would be risky, deployed 16 cannon and opened up on the Portuguese position. The defenders wavered, frightened by the sight and sound of the artillery more than the effect it had on their ranks, but they did not retreat because the Castilians had already sent some light cavalry around to their rear. Having nowhere to run, the Portuguese held their ground. The Castilians finally lost patience and charged, but a determined Portuguese defence won the day. Once again black powder had struck fear in the hearts of the enemy, but failed to be the deciding factor in battle. A fixed position of relatively exposed, massed men had been able to withstand an artillery barrage.
Castilian-French men-at-arms are forced to attack on a narrow front, where they are hammered by a blizzard of arrows from the flanks. Archaeological excavations of the battle site have revealed a network of defensive pits and ditches to protect the contingent of Anglo-Gascon archers fighting for the Portuguese; in addition, Froissart records that the archers cut down trees to make cavalry-proof fences.