When King Enrique learnt that the prince and his troops had made their way through the passes of Roncesvalles with the goodwill of the King of Navarre and that the latter had left the city of Pamplona and had cunningly had himself captured, he assembled his forces and went to pitch camp in a great forest of oaks near Santo Domingo de la Calzada. There he reviewed his troops, left again, crossed the Ebro and pitched camp again near the village of Añastro. There he was informed that some 6,000 of his best Castilian horsemen, whom he had sent to seize the town of Ágreda, which was opposed to him, had gone over to King Pedro. King Enrique was not, however, troubled by this but devoted every day to preparing his forces for battle.

The foreigners who were with him from Aragon were the following: Don Alfonso, son of Prince Pere and grandson of King Jaume; Don Felipe de Castro, a nobleman who was the brother-in-law of King Enrique, being married to his sister Doña Juana; Don Juan de Luna; Don Pedro Buil; Don Pedro Fernández de Iscar; Don Pedro Jordán de Urriés; and others. From France, the following knights were present there: Sir Bertrand du Guesclin; the Marshal of France; the ‘Stammerer’ of Villaines; and others. All the great lords and noblemen were there from Castile and León, except for Don Gonzalo Mejía and Don Juan Alfonso de Guzmán.

As King Enrique learnt that his enemies were approaching on foot, he drew up his battle-lines in the following way: in the vanguard, he placed Sir Bertrand and the other French knights to fight on foot; with them went the banner of the Order of the Sash, which was carried by Pero López de Ayala, followed by Don Sancho (the brother of King Enrique); Pero Manrique (the Chief Administrator of Castile); Pedro Fernández de Velasco; Gómez González de Castañeda; Juan Rodríguez; Pedro Ruiz Sarmiento; Ruy Díaz de Rojas; and other horsemen, so that there were up to 1,000 men-at-arms fighting on foot. On the left flank of the army, alongside those who were on foot, the king placed a wing of mounted men-at-arms, among them his brother Count Tello, Don Gómez Pérez de Porras (the Prior of San Juan) and other noblemen, so that there were up to 1,000 on horseback, with many of the horses clad in armour.