On the morning of the following day, the true dimension of the battle was revealed: in the field, the bodies of Castilians were enough to dam the creeks surrounding the small hill. In face of this, the Portuguese King offered the enemy survivors an amnesty and free transit home; an official mourning was decreed in Castile that would last until the Christmas of 1387. The French cavalry contingent suffered yet another defeat (after Crécy and Poitiers) by English defensive tactics, even though they finally defeated the English and unified their country after the 100 years war.

In October 1385, Nuno Álvares Pereira led a pre-emptive attack against Mérida, in Castilian territory, defeating an even larger Castilian army than at Aljubarrota in the battle of Valverde, in Valverde de Mérida. Scattered border skirmishes with Castilian troops would persist for five years more until the death of John I of Castile in 1390, but posed no real threat to the Portuguese crown; recognition from Castile would arrive only in 1411 with the signature of the Treaty of Ayllón (Segovia).

This victory assured that John of Aviz was the uncontested King of Portugal and the House of Aviz ascended to the crown of Portugal. In 1386, the closeness of relations between Portugal and England resulted in a permanent military alliance with the Treaty of Windsor, the eldest still active in existence.

His marriage to Philippa of Lancaster in 1387 initiated the Portuguese second dynasty, and their children went on to make historically significant contributions. Duarte, or Edward of Portugal, became the eleventh King of Portugal known as “The Philosopher” and “The Eloquent”, and his brother Henrique, or Henry the Navigator, sponsored expeditions to Africa.

In commemoration of the Battle of Aljubarrota the Portuguese erected the Monastery of Saint Mary of the Victory (Portuguese: “Mosteiro de Santa Maria da Vitória”) one of the best and original examples of Late Gothic architecture in Portugal, intermingled with the Manueline style.

In 1393 a chapel in honor of St. Mary and St. George was erected in the place where had been the standard of D. Nuno Alvares Pereira during the confrontation allowing us to know the precise geographic location of the confrontation site.

In 1958 archeologist Afonso do Paço organized the first campaign of excavations, revealing the complex defensive system consisting about 800 pits and dozens of defensive ditches and revealing one of the best preserved battlefields of the Hundred Years’ War.

In March 2002, under the initiative of António Champalimaud The Foundation Batalha de Aljubarrota was created. The Foundation began its activity by recovering the battlefield of Aljubarrota. Through a Protocol established with the Ministry of Defense, in August 2003, the Foundation received authorization to transform the Military Museum into a modern Interpretation Center of the Battle of Aljubarrota. This Interpretation Center was inaugurated in October 11, 2008.

On December 28, 2010, the Portuguese Official Journal published the Decret-Law n.º 18/2010, which states the legal recognition of the battlefield of Aljubarrota with the category of “national monument”.

Forces commanded by King John I of Portugal and his general Nuno Álvares Pereira, with the support of English allies, opposed the army of King John I of Castile with its Aragonese, Italian and French allies at São Jorge place, 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 as King of Portugal.

Portuguese independence was confirmed 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. To celebrate his victory and acknowledge divine help, John I of Portugal ordered the construction of the monastery of Santa Maria da Vitória na Batalha and the founding of the town of Batalha (Portuguese for “battle”,Portuguese pronunciation: [bɐˈtaʎɐ]). The king, his wife Philippa of Lancaster, and several of his sons are buried in this monastery, today a UNESCO World Heritage Site.

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 decimating 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 child of his marriage with Leonor Telles de Meneses was a girl, Princess Beatrice of Portugal.

In April of that same year the King signed the Treaty of Salvaterra de Magos with King Juan I of Castile. The treaty determined that Princess Beatrice was to marry Juan I, king of Castile, and the Crown of Portugal would belong to the descendants of this union. This situation left the majority of the Portuguese discontent, and the Portuguese nobility was unwilling to support the claim of the princess because that could mean the incorporation of Portugal to Castile^[a]; also the powerful merchants of the capital, Lisbon, were enraged from being excluded from the negotiations. Without an undisputed option, Portugal remained without king from 1383–85, in an interregnum known as the 1383–85 Crisis.

The first clear act of hostility was taken in December 1383 by the faction of John (João), the Grand Master of the Aviz Order (and a natural son of Peter I of Portugal), with the murder of Count Andeiro. This prompted the Lisbon merchants to name him “rector and defender of the realm”. However, the Castilian king would not relinquish his and his wife’s claims to the throne. In an effort to normalize the situation and secure the crown for him or Beatrice, he forced Leonor to abdicate from the regency. In April 1384, in Alentejo, a punitive expedition was promptly defeated by Nuno Álvares Pereira, leading a much smaller Portuguese army at the Battle of Atoleiros. This marked the first use of English defensive tactics on the Iberian peninsula, reportedly without any casualties to the Portuguese. A larger second expedition led by the Castilian king himself reached and besieged Lisbon for four months before being forced to retreat by a shortage of food supplies due to harassment from Nuno Álvares Pereira, and 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 (later King John I), regent of Portugal, reporting on negotiations, conducted in England, with John’s envoys – Dom Fernando, master of the order of Santiago, and Laurence Fogaça, chancellor of Portugal saying that an agreement had been reached under which an English force was to be sent to Portugal, to help defending the kingdom against its Castilian neighbor.^[2] On 6 April 1385, (the anniversary of the “miraculous” battle of Atoleiros, a fortuitous date), the council of the kingdom (cortes in Portuguese) assembled in Coimbra and declared him King John I of Portugal. After his accession to the throne, John I of Portugal proceeded to annex the cities in 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 host of 31,000 men to engage in a two-pronged invasion in May. The smaller Northern force sacked and burnt populations along the border, a common practice at the time and similar to what the English were doing in Scotland, before being defeated by local Portuguese nobles in 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 met with Nuno Álvares Pereira, the Constable of Portugal, in 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 allies arrived on Easter of 1385, consisting of a company of about 100 English longbowmen, veterans from the Hundred Years’ War, sent to honor the Anglo-Portuguese Treaty of 1373 (presently the oldest active treaty in the world). The Portuguese set out to intercept the invading army near the town of Leiria. Nuno Álvares Pereira took the task of choosing the ground for the battle. Russell notes that the two Portuguese leaders [Nuno Álvares and Antão Vasques] had already shown themselves masters of the new developments in methods of warfare, i.e. the use of archers and dismounted men-at-arms. The chosen location was São Jorge near Aljubarrota, especially indicated for the chosen military tactic, a small flattened hill surrounded by creeks, with the very small settlement of Chão da Feira (Fair’s Ground) at its widest point, still present today.