On 18 November 1282, Pope Martin IV opened proceedings against King Pedro of Aragon, because he had invaded the territory of Sicily, which was a papal fief, and was usurping the throne of Sicily, calling himself King.
On 18 November 1282, Pope Martin IV opened proceedings against King Pedro of Aragon, because he had invaded the territory of Sicily, in the wake of the Sicilian Vespers. Sicily was a papal fief, and, in the view of Rome, he was usurping the throne of Sicily, calling himself King.