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.

The first clear act of hostility was carried out 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.

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.

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 the bubonic plague.

[3] 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 whose military commanders supported Princess Beatrice and her husband's claims, namely Caminha, Braga, and Guimarães among others.

The smaller Northern force sacked and burnt towns along the border, before being defeated by local Portuguese nobles in the battle of Trancoso, in the first week of June.

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.

As in other defensive battles of the 14th century (Bannockburn (1314), Crécy (1346) or Poitiers (1356), for example), the dispositions were as following: dismounted cavalry and infantry in the centre with archers occupying the flanks.

The rear of the Portuguese position, which was in fact its front in the final 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.

Contrary to previous popular belief that Portuguese men-at-arms on John de Avis' side were badly equipped, and that his foot soldiers were almost with no armor, there's no reason to believe the Portuguese knightly class, even the ones that remained at Master de Avis' 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.

To calm the soldiers' nervousness and to improve his army's defensive position, general Nuno Álvares Pereira ordered the construction of a system of ditches, pits and caltrops.

This application of typical English tactical procedures had also been used by the Portuguese in the previous battle of Atoleiros and was especially effective against cavalry (the speciality of both the Castilian and the French armies).

[7] As was customary in many wars[citation needed][dubious – discuss] the French cavalry participated during this period, their impulsive advance proved catastrophic, as they were too far from the rest of the Castilian army to get any support, and were met uphill with obstacles, a narrow passage and a shower of arrows and crossbow bolts, which killed many horses, injured some men, and caused confusion.

On the other hand, as I have heard, the Castilians made no great haste to advance, for the French were not in good favour with them, and they had said, "Let them begin the fight, and tire themselves: they will find enough to do.

Conformably to this resolution, the Spaniards kept in a large body, twenty thousand at least, in the plain, and would not advance, which vexed the king much; but he could not help it, for they said, "My lord, it is all over, (though none had returned from the battle): these French knights have defeated your enemies: the honour and victory of the day are theirs.".

With all his troops needed at the front, there were no men available to guard the knight prisoners; John of Portugal ordered them to be killed on the spot and proceeded to deal with the approaching Castilians.

According to Froissart, however, Avis' war council decided to slay their prisoners before the main body of Castile arrived, after the French cavalry failure, killing many knights, esquires and non-noble men-at-arms.

The Castilian knights in the main body were forced to dismount and break in half their four-metre-long lances in order to join the constricted melèe alongside their infantry.

When the Castilian royal standard-bearer fell, the already demoralized troops in the rear thought their King was dead and started to flee in panic; in a matter of moments this became a general rout where Juan of Castile had to run at full speed to save his life, leaving behind not only common soldiers but also many still dismounted noblemen.

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

Through a protocol established by 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.

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".