On May 29, 1453 Constantinople fell to the Ottomans, but Venice managed to maintain a colony in the city and some of the former trade privileges it had had under the Byzantines. Indeed, in 1454, the Ottomans granted the Venetians their ports and trading rights. Despite the recent Ottoman defeats by John Hunyadi of Hungary and by Skanderbeg in Albania, war was unavoidable. In 1463 the Venetian fortress of Argos was ravaged. Venice set up an alliance with Matthias Corvinus of Hungary and attacked the Greek islands by sea and Bulgaria by land. The allies were forced to retreat on both fronts, however, after several minor victories. Operations were reduced mostly to isolated ravages and guerrilla attacks, until the Ottomans moved on a massive counteroffensive in 1470: this resulted in Venice losing its main stronghold in the Aegean Sea, Negroponte. The Venetians sought an alliance with the Shah of Persia and other European powers, but, receiving only limited support, could make only small-scale attacks at Antalya, Halicarnassus and Smirne.