The Battle of Aljubarrota was fought between the Kingdom of Portugal and the Crown of Castile on 14 August 1385. Forces commanded by King John I of Portugal and his Constable Nuno Álvares Pereira, with the support of English allies, opposed the army of King John I of Castile with its Aragonese and French allies, as well as Genoese mercenaries at São Jorge, between the towns of Leiria and Alcobaça, in central Portugal. The result was a decisive victory for the Portuguese, ruling out Castilian ambitions to the Portuguese throne, ending the 1383–85 Crisis and assuring John's position as King of Portugal.
Portuguese independence was safeguarded and a new dynasty, the House of Aviz, was established. Scattered border confrontations with Castilian troops would persist until the death of John I of Castile in 1390, but these posed no real threat to the new dynasty.
Prelude
The end of the 14th century in Europe was a time of revolution and crisis, with the Hundred Years' War between the English and the French for Western France, the Black Death devastating the continent, and famine afflicting the poor. Portugal was no exception. In October 1383, King Ferdinand I of Portugal died with no son to inherit the crown. The only surviving child of his marriage with Leonor Telles de Meneses was a girl, Princess Beatrice of Portugal.
In April of that same year Ferdinand had signed the Treaty of Salvaterra de Magos with King Juan I of Castile. The treaty determined that Beatrice was to marry Juan, and the Crown of Portugal would belong to the descendants of their union. This situation left the majority of the Portuguese discontented, and the Portuguese nobility was unwilling to support the claim of the princess as that could lead to the incorporation of Portugal into Castile. Also, the powerful merchants of the capital, Lisbon, were enraged at being excluded from the negotiations. Without an undisputed option, Portugal remained without a king from 1383–85, in an interregnum known as the 1383–85 Crisis, with Queen Leonor acting as regent for her ten-year-old daughter.
The first clear act of hostility was carried out in December 1383 by the faction of John (João), the Grand Master of the Military Order of Aviz (and a natural son of Peter I of Portugal), with the murder of João Fernandes Andeiro, the Count of Ourém, adviser and lover of Queen Leonor. This prompted the Lisbon merchants to name John "rector and defender of the realm". However, the Castilian king would not relinquish his and his wife's claims to the Portuguese throne. In an effort to normalize the situation and secure the crown for himself or Beatrice, he forced Leonor to abdicate from the regency. In April 1384, in Alentejo, a punitive Castilian expedition was promptly defeated by Nuno Álvares Pereira, leading a much smaller Portuguese army at the Battle of Atoleiros. This was an example of the use of the defensive tactic of forming an infantry square to repel cavalry, reportedly without any casualties to the Portuguese.
A larger second expedition led by the Castilian king himself reached and besieged Lisbon for four months in the summer of 1384, before being forced to retreat by a shortage of food supplies due to harassment from Nuno Álvares Pereira, and an outbreak of the bubonic plague.
In order to secure his claim, John of Aviz engaged in politics and intense diplomatic negotiations with both the Holy See and England. In October 1384, Richard II wrote to John, reporting on negotiations conducted in England with John's envoys (Dom Fernando, master of the order of Santiago, and Laurence Fogaça, chancellor of Portugal), confirming that an agreement had been reached under which a small English contingent was to be sent to Portugal to help defend it against Castile (an ally of France at this time). On 6 April 1385, (the anniversary of the "miraculous" battle of Atoleiros, a fortuitous date), the Portuguese Cortes assembled in Coimbra and acclaimed John of Aviz as King John I of Portugal. After his accession to the throne, John proceeded to annex the cities whose military commanders supported Princess Beatrice and her husband's claims, namely Caminha, Braga, and Guimarães among others.
Enraged by this "rebellion", Juan I ordered a two-pronged invasion of Portugal in May 1385 by an army of 31,000 men. The smaller northern force sacked and burnt towns along the border, before being defeated by local Portuguese nobles at the battle of Trancoso in the first week of June. On the news of the invasion by the Castilians, John I of Portugal's army joined with the forces led by Álvares Pereira (now Constable of Portugal) at the town of Tomar. There they decided to face the Castilians before they could get close to Lisbon and lay siege to it again.
English mercenaries arrived from Gascony at Easter 1385, sent to honor the Anglo-Portuguese Treaty of 1373 (still the oldest active international treaty in the world). This company was composed of about 200 English longbowmen, veterans from the Hundred Years' War, and around 500 locally recruited men-at-arms mostly of English and Gascon background, though a Florentine volunteer was also mentioned.
The Portuguese and their allies set out to intercept the invading Castilian army near the town of Leiria. Álvares Pereira took on the task of choosing the ground for the battle. Russell notes that two Portuguese generals (Nuno Álvares Periera and Antão Vasques de Almada) had already shown themselves masters of the new developments in methods of warfare, i.e. the combined use of archers and dismounted men-at-arms on the defensive. The chosen location was São Jorge near Aljubarrota, especially suitable as a defensive position, being a small flattened hill surrounded by creeks with the small settlement of Chão da Feira at its widest point, still present today.
By placing his army on the road to Lisbon, John of Aviz effectively distracted John of Castile from laying siege to the capital itself, forcing the Castilians to offer battle there on Portuguese terms. As in the Battle of Agincourt, winning this pitched battle would mean a decisive victory for Aviz's cause, even with smaller numbers and resources.
Portuguese dispositions
At around 10 o'clock in the morning of 14 August 1385, the army of John of Aviz took its position at the north side of this hill, facing the road where the Castilians would soon appear. As in other defensive battles of the 14th century (Bannockburn (1314), Crécy (1346) and Poitiers (1356), for example), the dispositions were as following: dismounted cavalry and infantry in the centre with archers occupying the flanks. Notably, on the vanguard's left wing (later covering the left flank), a company composed by some two hundred unmarried young nobles is remembered to history as the "Ala dos Namorados" (Lovers' Flank); the right wing, also two hundred strong, known as "Ala de Madressilva" or Honeysuckle Flank, did not achieve the same heroic fame. On either side, the army was protected by natural obstacles, in this case creeks and steep slopes. In the rear, reserve forces were at hand, commanded by John of Aviz himself. In this elevated position, the Portuguese could observe the enemy's arrival and were protected by a steep slope in their front. The rear of the Portuguese position, which became its front later in the battle, was at the top of a narrow slope which came up to a small village, and was further defended by a complex series of interlocking trenches and caltrops designed to surprise and trap the enemy cavalry. These field fortifications were used extensively by both the English in France and the Portuguese in the rare set-piece battles of the Crisis of the Succession.
Contrary to previous popular belief that the Portuguese men-at-arms with John of Aviz side were badly equipped, and that his foot soldiers were almost unarmored, there is no reason to believe the Portuguese knightly class, even the ones on Aviz's side — as most of the upper nobility supported John of Castile - were not able to afford the knightly harness expected in the same Iberian standards of its time. And while the Portuguese primary sources use the comparative inferiority of Portuguese equipment to increase the glory of their victory, this should be considered in light of the fact that most of the fighting by the Castilian side involved heavily armored men-at-arms, and by jinetes (light cavalry) armed with at least a combination of mail and padded armor.
Frei Pedro, in his sermon given at Lisbon after the battle, describes the Portuguese equipment: "The Portuguese [...] were poorly and badly armed; here, the one that had mail armor didn't have padded armor, and the one that had a cuirass didn't have arm harness, and many of them with open-faced bascinets. So that if all their arms were matched as they should, it won't equip a third of the people". While this equipment would be inferior to the standards expected from a man-at-arms, it would otherwise be quite adequate for actual infantry, which composed most of Lisbon's host. Other sources mention Portuguese arms as: "everyone's defensive arms were bascinets with camail, either open-faced or with visor, and coats of plates, padded armor, mail shirts, mail skirts and cuirasses; and for offensive spears and pollaxes of iron and lead, and axes for those who could have them".
Castile arrives
The Castilian vanguard arrived from the north around midday. Seeing the strong defensive position occupied by the Portuguese, John of Castile decided to avoid combat on John of Portugal's terms. Due to the size of the Castilian army, it slowly started to contour around the hill where the Portuguese were. Castilian scouts had noticed that the south side of the hill had a gentler slope and it was there that the Castilian king wanted to attack.
In response to this movement, the Portuguese army reversed its position and headed to the south slope of the hill. Since they were fewer than the enemy and had less ground to cover, they reached their final position very early in the afternoon. To calm the soldiers' nervousness and to improve his army's defensive position, Álvares Pereira ordered the construction of defensive ditches, pits and caltrops. This application of contemporary English tactical procedures had also been used by the Portuguese at Atoleiros and was especially effective against cavalry (the specialty of both the Castilian and the French armies).
Around six o'clock in the afternoon the Castilian army was finally ready for battle. According to John of Castile's report of the battle, his soldiers were by then very tired from the march that had started early in the morning under a blazing August sun. There was no time to halt then, and the battle would soon begin.
Battle
The initiative of starting the battle was with the Castilian side. The French allied heavy cavalry charged in full strength, in order to disrupt the enemy lines. According to Jean Froissart, based on visual testimonies of the battle: "The French knights amounted to two thousand, as gallant lances as could be seen. The moment they perceived the enemy they formed in close order, like men of resolution who knew their business, and advanced within bow-shot".
As was frequent in many battles during this period, the impulsive charge of the French cavalry proved disastrous, as they were too far ahead of the rest of the Castilian army to receive any support, and were charging uphill at a narrow fortified defensive position while being pelted with showers of arrows and crossbow bolts, which killed many horses, injured some men, and caused confusion. The French, however, being heavily armored, were still able to enter close combat with the Portuguese vanguard, where heavy fighting ensued with the dismounted Portuguese and Anglo-Gascon men-at-arms. The losses of the French cavalry were heavy and the effect of its attack completely null. Support from the Castilian rear was late to come and the knights that did not perish in the combat were made prisoners and sent to the Portuguese rear.
Froissart claims envy was the reason behind why the Spaniards were undisposed to help the French, held to be the best heavy cavalry of Europe, and highly prized by the King of Castile himself: