Battle of Épila The Battle of Épila was fought on July 21 , 1348 near Zaragoza , in what is now Spain , between the supporters of the Union of Aragon and King Peter IV , led by Don Lope de Luna . This battle was the culmination of a long confrontation between a large segment of the nobility and the people of Aragon against the king , ending with the decisive defeat of the Union . Background . The start of direct conflict between the King of Aragon and much of the nobility and the towns of the kingdom went back to the year 1282 , following the conquest of Sicily by Peter III and his excommunication by Pope Martin IV and subsequent Aragonese Crusade . To achieve more effective pressure on the king and protect each other , the nobility of Aragon signed the Oath of the Union , in which they pledged support for each other against the king of Aragon in the event he attempted to undermine their privileges . The first noble rebellion was later expanded to include the Union of Aragon and major cities , including the city of Zaragoza , capital of the Kingdom of Aragon . Following the meeting of the Cortes in Zaragoza in 1283 , Peter III was forced to accept the demands of the General Privilege of the Union , which expanded in 1287 during the reign of his son Alphonso III regarding the privileges of the Union . The Union against Peter IV . Peter IV had become king of Aragon in 1336 , following the death of his father Alfonso IV . His first major domestic problem occurred in 1347 with the reactivation of the Union of Aragon . The original purpose of the confrontation was in Peter IV ' s decision to acknowledge his daughter Constance as heiress to the Crown of Aragon , which infringed the rights of the " Infante " James , his own brother . As acting Governor of Aragon , James immediately went to Zaragoza to seek the support of the Aragonese nobility against the royal decision . The rebelling nobles again swore allegiance to the Union in support of the " Infante " movement ; to which the majority of municipalities soon joined , including the capital . There was also a similar Union organized in the Kingdom of Valencia . At first Peter IV sought to resolve the situation by resorting to diplomacy : Cortes convened in Zaragoza and gave their revocation of his decision and instead agreed to confirm the privileges of the Union of 1287 . From that moment , the only possible solution was armed conflict . Following the Cortes decision , " Infante " James died in Barcelona , possibly poisoned by order of Peter IV . At the end of 1287 , fighting occurred in the two kingdoms of Aragon and Valencia : First , the Union of Valencia defeated the royalists at Largo and Bétera , but in Aragon , King Peter IV attracted major Aragonese nobles like Lope de Luna and the village communities of Daroca and Teruel to his aid . In early 1348 , Peter IV managed to reach an agreement with the Valencian Union so that any military activity was concentrated thereafter in the Kingdom of Aragon . The battle . By the spring of 1348 the Unionists had concentrated all their forces in Zaragoza , reluctant to work with the nobles who still supported the king . For his part , Lope de Luna attempted to take the city of Tarazona , a member city of the Union . In early July , Peter IV , with the kingdom of Valencia pacified and the support of the inhabitants of Teruel , Daroca and Calatayud , marched on Zaragoza intending to end the revolt . The Unionists , realizing they could not cope with the united forces of Peter IV and Lope de Luna , tried to cut them off , taking a central location that was in the hands of the royalists , the village of Épila . Lope de Luna understood that if the Unionists took Épila he would be blocked and unable to receive support from King Peter . Therefore , Lope de Luna immediately left the siege of Tarazona and force - marched towards Épila to stop the Unionist Army . < br > There followed the final battle on July 21 , 1348 . Royal Army . " ' In Épila " ' " ' Army of Lope de Luna " ' Union Army . Development . The battle began on the morning of July 21 with an attempt by Union troops , led by Juan Ximénez de Urrea , Jr . , to occupy Épila . Blasco de Alagon had taken refuge inside Épila , his mission was to defend the place until the core troops of Peter IV joined with those of Lope de Luna . The frontal attack was very intense but the Unionists lacked sufficient troops to overcome the defenses and did not have time to prepare , knowing that Lope de Luna had left the siege of Tarazona and was marching towards Jalón to force a confrontation . Repulsed at their first assault , the Unionists burned the crops and the suburbs in an attempt to force a showdown in the open . The center of the battle was the bridge over the Jalón river . Unionists tried to hold it until Castilian mercenaries commanded by Gómez de Albornoz arrived . The inexperienced laborers of Zaragoza could not stop several hundred well armed and experienced horsemen . The Castilian mercenaries not only made their way to the other side but directly attacked the rebellious Aragonese nobles who remained in reserve . Some of the Aragonese immediately took flight as the Unionist troops were unable to halt the cavalry . Only those most committed to the noble cause entered the battle with the intention of withstanding until nightfall . But eventually resistance broke , causing the deaths or capture of the principal leaders of the Aragonese Union . Consequences . The victory of the royalist troops at the battle of Épila was complete and final . Those killed were the chief supporters of the Union ; Juan Ximénez de Urrea , Lord of Biota , Tramacet Jimen Gombal and Perez de Pina . The prisoners were : Juan Ximénez de Urrea , son of the former , who had led the Union army in the action at Valencia and was executed a few days later ; and Pedro Fernandez , Lord of Híjar . " Infante " Ferdinand himself , who had been captured by Castilian soldiers , was sent to Castile , fearing that Peter IV would order him executed . King Peter IV convened the Cortes in Zaragoza and awarded the title of " Count " to Lope de Luna , the first nobleman in Aragon to get this title without belonging to the royal family . On October 4 , 1348 , the Parliament of Aragon revoked all privileges and rights of the Unionists and Peter IV destroyed the documents of the collected privileges . However , the king extended the powers of the Justice of Aragon to mediate conflicts between the Aragonese and the monarch , so that much of the rights that the nobles , which had been attributed to the Union , were safeguarded in the figure of Justice and extended to all the Aragonese .