THE dominance that Pere of Aragon had achieved over the Trencavel by the early thirteenth century made his response to the crusaders’ attack on Béziers and Carcassonne particularly crucial. Pere might have been expected to save Raimond Roger from his fate; in the event, the king's reaction to the crusaders allowed them to seize the Trencavel lands. The ambivalence of Pere's position when it came to the crusade's treatment of the Trencavel reflects his general attitude towards the crusade. On the one hand, he fully supported its aims, having been an enthusiastic prosecutor of heresy in Aragon itself and a somewhat more circumspect one in Languedoc. He showed himself to have a keen appreciation of the merits of crusading against enemies of the faith in Europe, as demonstrated by his participation in the campaign against the Muslims in Spain in 1212, which culminated in the victory of Las Navas de Tolosa, and also enjoyed cordial relations with the leader of the crusade, Arnauld Amaury, which dated back to the latter's abbacy at Poblet.

On the other hand, however, he was clearly concerned that the crusaders could threaten his own lands in Languedoc. In September 1209 Innocent III wrote to Berenguer, Archbishop of Narbonne and Pere, Bishop of Barcelona, giving them permission to excommunicate anyone who took any lands belonging to the King of Aragon. The timing of this letter, written at the time of the first campaign undertaken by the crusaders against Pere's towns of Béziers and Carcassonne, indicates that it was sent in response to Pere's concerns that his property in Languedoc would not be safe from the depredations of the crusaders. It suggests that Pere was not a wholehearted supporter of the crusade even at its inception; although he approved of its aims, he was inevitably concerned that those very laudable goals might be to the detriment of his power in Languedoc.

Pere's concerns about the incursions of the crusade into his own lands in Languedoc were to lead eventually to his military support for the counts of Toulouse, Foix and Comminges and to his defeat and death at the Battle of Muret in 1213.