SO WHY WAS there a pitched battle at Aljubarrota? What led two royal armies to settle an old quarrel in a very short space of time, in a pitched battle that they both knew would be decisive? Why did the two monarchs not opt for a Vegetian-type strategy, which was suggested to both by many of their counsellors? To what extent can the “modified Gillingham paradigm” be applied to the specific case of São Jorge?

The Political Circumstances

Let us start by considering the situation of both parties at the start of August 1385. On the side of João I of Portugal, we have a very fragile political-military position, due to a recent and hotly disputed enthronement (at the Cortes de Coimbra) and the existence of a divided kingdom, where a great number of fortresses, particularly close to Lisbon (such as the well-protected Santarém), supported his adversary. This viewpoint was aggravated by a clear inferiority of military and financial resources, which made the political cause of the ex-Master of Avis dependent on support from England. Added to all this was the conviction that it would be difficult to withstand a Castilian attack on the capital, since Lisbon (considered the key political and military location in the kingdom) was ill-prepared to resist a new siege.

The Portuguese king had in his favour the fact that the invasion of Portugal by Juan I constituted a violation of the 1383 agreements which underwrote Leonor Teles's regency. As Suárez Fernández has shown, Juan I of Castile, a member of the House of Trastámara moved beyond the strategies of his father, Enrique II, who sought matrimonial alliances with all the ruling houses of the Iberian Peninsula, into a desire to dynastically absorb Portugal. In doing so, he acted in a premeditated way, signing agreements that he had no intention to comply with and seeking the conquest of the Lusitanian throne without respecting the treaties signed shortly before the death of King Fernando. This despite the warnings—according to the chronicler López de Ayala—which were given to him by some of his counsellors at Puebla de Montalbán.