A major obstacle to this was represented by the conflict between the French Capetian House of Anjou ruling southern Italy and the Kingdom of Aragon in Spain. In 1282, the citizens of Palermo rose up against Charles of Anjou and turned for help to Peter III of Aragon, in what has become known as the Sicilian Vespers. In the war that followed, Charles of Anjou's son, Charles of Salerno, was taken prisoner by the Aragonese. The French began planning an attack on Aragon, raising the prospect of a large-scale European war. To Edward, it was imperative that such a war be avoided, and in Paris in 1286 he brokered a truce between France and Aragon that helped secure Charles's release. As far as the crusades were concerned, Edward's efforts proved ineffective. A devastating blow to his plans came in 1291, when the Mamluks captured Acre, the last Christian stronghold in the Holy Land. Edward had long been deeply involved in the affairs of his own Duchy of Gascony. In 1278 he assigned an investigating commission to his trusted associates Otto de Grandson and the chancellor Robert Burnell, which caused the replacement of the seneschal Luke de Tany. In 1286, Edward visited the region himself and stayed for almost three years. The perennial problem was the status of Gascony within the Kingdom of France, and Edward's role as the French king's vassal. On his diplomatic mission in 1286, Edward had paid homage to the new king, Philip IV, but in 1294 Philip declared Gascony forfeit when Edward refused to appear before him in Paris to discuss the recent conflict between English, Gascon, and French sailors that had resulted in several French ships being captured, along with the sacking of the French port of La Rochelle. Correspondence between Edward and the Mongol court of the east continued during this time. Diplomatic channels between the two had begun during Edward's time on crusade, regarding a possible alliance to retake the Holy Land for Europe. Edward received Mongol envoys at his court in Gascony while there in 1287, and one of their leaders, Rabban Bar Sauma, recorded an extant account of the interaction. Other embassies arrived in Europe in 1289 and 1290, the former relaying Ilkhan Abaqa's offer to join forces with the crusaders and supply them with horses. Edward responded favourably, declaring his intent to embark on a journey to the east once