After the
Treaty of Brétigny favorable to England was signed in 1360, ending the Edwardian phase of the Hundred Years' War, France tried to avoid open conflict with England and tried to associate with Castile to gain an advantage. France had to find employment for the mercenaries of the great companies dedicated to pillage now that there was no war. In late 1365,
Charles V of France, with the help of
Pope Urban V, succeeded in diverting temporarily most of the great companies. Under the pretext of carrying on a crusade against the Moorish
Kingdom of Granada, the Pope paid for an expedition to Spain. Later on, France and Aragon paid to recruit these troops for Henry's cause, removing the free companies from France and supporting the ascent to power in Castile of their favorite. The strength of the army of Henry rested primarily on these companies, groups of mercenaries that had participated in the Hundred Years' War, composed mainly of Bretons, Gascons, English and French. The Black Prince (Edward, Prince of Wales and Duke of Aquitaine) was the main beneficiary of the peace treaty of 1362 between England and Castile that allowed Castile to keep safe maritime trade routes and in turn England kept herself safe from the large Castilian war fleet. Edward did not seem interested in prohibiting the participation of his Gascon and English subjects in the Castilian Civil War on the side of the pretender Henry, although it favoured France and was against the interests of England. Aquitaine was going through a difficult stage as the main funding sources for this traditionally poor region were the wine industry (which was depressed) and warfare. Aquitaine no longer received subsidies from England and needed other sources of revenue. England would not allow France to ally with Castile to establish Henry as the new king. When Peter I of Castile, who was losing the war against his stepbrother Henry and his mercenary troops, sought help,
King Edward III of England ordered
Sir John Chandos the constable of Aquitaine and other commissioners to ensure that the Gascon and English mercenaries stopped assisting Henry. In February 1366, England sent several Gascon great companies to strengthen the position of King Peter but these measures proved insufficient and Peter had to flee Castile.
Army composition England then decided to recruit a huge army of mercenaries to support the cause of King Peter of Castile, with the incentive of plundering the riches of Castile. The Black Prince brought together a diverse and colossal army of
Gascon,
Poitevins and
English nobles as well as distinguished mercenary troops consisting of the most famous captains of great companies that had struggled in recent years. These came mainly from Gascony but also from
Brittany,
Navarre,
Foix,
Germany (
Holy Roman Empire),
England,
Calais, the County of
Poitou,
Hainault and elsewhere, including mercenaries who had served Henry of Trastámara in his ascension to the throne. With the mercenaries back in France, they aided the cause of his enemy, King Peter. This army probably numbered around 8,000 to 10,000 men, something similar to the previous
Battle of Poitiers. There were also Castilians loyal to Peter, about 400 English archers recruited by
John of Gaunt, some
Aragonese unhappy with their king and the troops of King
James IV of Majorca. In August 1366, King Peter of Castile, the Prince of Wales, and King
Charles II of Navarre met in
Bayonne, to agree on the terms of an invasion. The King of Navarre would allow the invading army passage from Aquitaine to Castile through Navarre, for which he would be well paid. Peter, who was willing to accept all conditions, was also to reimburse the expenses of the army recruited by the Prince of Wales and offer Castilian territories to be annexed to his duchy of Aquitaine. Henry had dismissed almost all his troops, because of the tremendous expense that led him to keep his mercenary army in the rise to power. These troops roamed Castile committing outrages or changed sides. Henry came to an agreement with King Charles II of Navarre that Charles would, in exchange for a reward, block the Pyrenean pass from France to Castile, something that could be done easily with a few men. Charles was either betting on two horses or feared facing Castile and Aragon. In February 1367, the English mercenaries of
Hugh Calveley, who remained in the peninsula and worked for Henry, switched sides and overran several towns of Navarre from the south in a
chevauchée. This forced the King of Navarre (Charles II) to open the way for the army of the Black Prince and to provide 300 men for their cause, a minimal amount to pretend he was on their side. To avoid to go to the battle in person, the King of Navarre faked his own capture during a hunt in collusion with captain Olivier de Mauny, cousin of Bertrand Du Guesclin, the Lieutenant of Henry's army. When Henry heard of the entrance of the Black Prince's army to the peninsula he enlisted all the troops he could and sent
Bertrand Du Guesclin immediately from
Zaragoza back to Castile with his best captains, although most of their forces had to stand to protect
Aragon from the Black Prince's army. No more than 1,000 French
men-at-arms reinforced Henry's army along with some Aragonese nobles. From the mountains,
Biscay,
Gipuzkoa and
Asturias came footsoldiers but they did not participate in the battle.
Army strength The commonly accepted version among historians is the version of the chronicles of Pedro Lopez de Ayala in which the army of Peter, supported by the Black Prince, consisted of more than 10,000 men, most of them the best mercenaries that could be found in Europe, and the army of Henry had 4,500 men of which 1,000 were elite mercenaries from France. Another source is the unreliable chronicle of Jean Froissart, known for his Anglophilia, whose data should not be taken too seriously in this battle, because he was not even in Spain at that time. According to Froissart, the Castilian-French army had 76,000 men. Some British historians have raised the numbers to 86,000 men. According to Froissart the Anglo-Castilian army had 24,000 men.
Previous encounters During March, despite his huge disadvantages, Henry had great success using guerrilla tactics and skirmishing against the army of the Black Prince. Castilian troops had great offensive power and greater mobility thanks to their lighter armament, something that made them ideal for this type of action, unlike the slow and heavily armored army of Peter, composed mainly of heavy infantry and heavy cavalry. He was an experienced soldier, having fought in France as a great company commander against the English and knew that the best military strategy to take on the huge army of the Black Prince, was the wear it down with the harsh Castilian lands, hunger and the skirmishes. These were also the recommendations of the King of France and of Bertrand du Guesclin. The light cavalry was an old tradition in Castilian military systems and was designed for the frequent skirmishes with the Moors, even though the idea had been abandoned by other European armies of that time. In the small Battle of
Aríñez (Basque,
battle of Inglesmendi, Battle of the English Mount) in the third week of March 1367, a vanguard of Henry's army formed by
jinetes (Castilian light cavalry) led by Don Tello and Aragonese and French knights led by
Arnoul d'Audrehem,
Pierre le Bègue de Villaines and
Juan Ramirez de Arellano wiped out a detachment of the Black Prince's army. Henry's vanguard easily defeated groups ahead of the bulk of the army of the Black Prince by skirmishes and then headed back to their base. On their way, they met with an exploration detachment of the Black Prince's army, which was led by the Seneschal of Aquitaine Sir
Thomas Felton with 200 men-at-arms and archers. After suffering many casualties, the detachment of the Prince of Wales entrenched in the mountain of Inglesmendi, where the English longbowmen resisted the Castilian light cavalry. The French and Aragonese soldiers dismounted and attacked as infantry, defeating them. There died, among others,
Sir William Felton, Seneschal of Poitou and captain of great companies; many others were captured, Thomas Felton, the captain of great companies,
Richard Taunton, Sir
Hugh Hastings, the military
Lord John Neville, the captain of great companies Aghorises and the Gascon mercenary captain of great companies
Gaillard Vighier (or Beguer), among others. The army of the Black Prince that had hitherto been considered invincible, had suffered its first defeat and although their losses were not large in comparison with the large army, the troops began to become demoralized. The Black Prince mobilized his troops to approach
Burgos—his goal—from
Vitoria, but Henry stepped ahead and blocked his path which forced the army of Peter to retreat again. At the end of March the Black Prince crossed the Ebro at
Logroño, where he made a camp. Henry again blocked access to Burgos by controlling the
river Najerilla. The political situation was quite different; more people adhered to the cause of Peter that gained strength, while his alliances weakened, because avoiding confrontation was seen as a sign of weakness by the Castilian nobility. Time was playing against the ambitious Henry, who advanced with his forces, leaving behind the protection of the river Najerilla to confront his half-brother. To prevent disaster, he had to face the most prominent mercenary troops of Europe, outnumbered, in a battle in the open and with the river in his back cutting his retreat, despite the opposition of Bertránd du Guesclin and the rest of his field commanders. ==Battle==