The attempt of the Genoese merchants at Caffa to exclude the Venetians from the lucrative free trade with the Tartars led to numerous quarrels in the Black Sea, and [Sidenote: War of Venice and Genoa, 1350-5.] ultimately to open warfare between the two states. Venice secured the support of John Cantacuzene, the Greek emperor, who disliked Genoese dictation at Pera, and of Peter of Aragon, who was contending with Genoa for the possession of Sardinia. In 1352 Niccolo Pisani, with a powerful fleet of Venetian, Greek, and Catalan vessels, sailed to attack Pera, which was defended by the Genoese admiral, Paganino Doria. In the narrow waters of the Bosphorus the allies were unable to make full use of their numbers, and a furious storm threw their vessels into such disorder that they did more harm to each other than to the enemy. Pisani was forced to retire, but Doria, though victorious, had suffered such losses that he was superseded by Antonio Grimaldi. In 1353 the Aragonese, who had fewer interests in the Levant than their allies, insisted upon transferring hostilities to the coast of Sardinia. In the open water off Cagliari the Venetians and Catalans gained a complete victory, and Grimaldi with difficulty escaped to carry the news of this crushing disaster to Genoa. Pisani was too weakened by the encounter to venture a direct attack upon Genoa, but the Genoese were so panic-stricken that they offered the lordship of the city to Giovanni Visconti, in order to gain the aid of Milan. Venice replied to this move by an alliance with the opponents of Milan on the mainland, but the struggle continued to be fought out at sea. Paganino Doria, restored to the command after Grimaldi’s defeat, once more carried the war into eastern waters. Pisani, after an uneventful campaign in 1354, had retired into winter quarters at Portolungo on the coast of the Morea, under the shelter of the island of Sapienza. There the Venetians were surprised by Doria, and their fleet was completely annihilated (November 4, 1354). The battle of Sapienza was the most decisive engagement of the struggle. It was followed by the conspiracy and death of Marin Falier, and the Venetians were so discouraged by the combination of external defeat and domestic treason that they concluded peace with Genoa in 1355. All demands for concessions in the Black Sea were abandoned, and Genoa retained its superiority in the northern trade.