Pope Martin IV
During Dandolo's reign as doge, relations with the Vatican were tense. Venice had refused to join the Papal States in a punitive action against Sicily, provoking Pope Martin IV to excommunicate Venice, which was later repealed in 1285 by Martin's successor, Pope Honorius IV. In 1287 unrest flared up again in Istria and spread to Friuli. The war widened after the intervention of the German Emperor Rudolf I, who was allied with the Patriarchate of Aquileia, and Venice had to sue for peace.