Aragonese Crusade The Aragonese Crusade or Crusade of Aragon , a part of the larger War of the Sicilian Vespers , was declared by Pope Martin IV against the King of Aragon , Peter III the Great , in 1284 and 1285 . Because of the recent conquest of Sicily by Peter , the Pope declared a crusade against him and officially deposed him as king , on the grounds that Sicily was a papal fief : Peter ' s grandfather and namesake , Peter II , had surrendered the kingdom as a fief to the Holy See . Martin bestowed it on Charles , Count of Valois , son of the French king , Philip III , and nephew of Peter III . The conflict quickly became a kind of civil war , as Peter ' s brother , King James II of Majorca , joined the French . James had also inherited the County of Roussillon and thus stood between the dominions of the French and Aragonese monarchs . Peter had opposed James ' inheritance as a younger son and reaped the consequence of such rivalry in the crusade . In 1284 , the first French armies under Philip and Charles entered Roussillon . They included 16 , 000 cavalry , 17 , 000 crossbowmen , and 100 , 000 infantry , along with 100 ships in south French ports . Though they had James ' support , the local populace rose against them . The city of Elne was valiantly defended by the so - called " Bâtard de Roussillon " ( Bastard of Roussillon ) , the illegitimate son of Nuño Sánchez , late count of Roussillon ( 1212 – 1242 ) . Eventually he was overcome and the cathedral was burnt , despite the presence of papal legates , while the population was massacred , all save the " Bâtard " . He succeeded in negotiating his surrender and accompanied the advancing royal forces as a prisoner . In 1285 , Philip the Bold entrenched himself before Girona in an attempt to besiege it . The resistance was strong , but the city was taken . Charles was crowned there , but without an actual crown . On 28 April , Cardinal Jean Cholet placed his own hat on the count ' s head . For this , Charles was derisively but not unaffectionately nicknamed " roi du chapeau " ( " king of the hat " ) . The French soon experienced a reversal , however , at the hands of Peter III ' s admiral , Roger de Lauria . The French fleet was defeated and destroyed at the Battle of Les Formigues . As well , the French camp was hit hard by an epidemic of dysentery . Philip himself was afflicted . The heir to the French throne , Philip , opened negotiations with Peter for free passage for the royal family through the Pyrenees . But the troops were not offered such passage and were decimated at the Battle of the Col de Panissars . The king of France himself died at Perpignan , the capital of James of Majorca , and was buried in Narbonne . Peter did not long survive him . Historian H . J . Chaytor described the Aragonese Crusade as " perhaps the most unjust , unnecessary and calamitous enterprise ever undertaken by the Capetian monarchy . " W . C . Jordan has blamed it for the attitude the young Philip took towards papal interference in French foreign policy upon his succession : a view with long - reaching consequences for Europe . The crusade ' s legacy to France was slight , but Majorca was devastated as an independent polity . Peter ' s son Alfonso III annexed Majorca , Ibiza , and Minorca in the following years . In 1295 , the Treaty of Anagni returned the islands to James and the Treaty of Tarascon of 1291 officially restored Aragon to Alfonso and lifted the ban of the church .