Cantacuzenus asked for the aid of the Genoese, who joined him in order to resist the Venetians. The rivalry during this reign between the two republics of Venice and Genoa was great. Each was at the height of its power, and the commerce and dominions of the empire were the principal objects of their rivalry. A hundred and fifty years earlier there had been colonies of Amalfians, Pisans, Anconans, Ragusans, and even Germans, within the walls of the city. All these had disappeared,[60] and Genoa the Superb and Venice, Queen of the Seas, were the sole Italian competitors for domination in or a share of the empire. At the period with which we are concerned they were about equally matched in strength, and the two brave republics were constantly fighting the battles of their great duel in the waters of the Greek empire. Within a few months the Genoese were alternately the allies and the enemies of Cantacuzenus. In 1350 a fleet of fourteen Venetian galleys, and another of Catalans, prevented the Genoese from entering the Bosporus. Two years later another formidable fleet of Venetian galleys joined one of twenty-six Spaniards in order to attack the Genoese. After Pisani, the Venetian admiral, had rested his men for two days on the island of Prinkipo, he joined the imperial ships at Heptaskalion, and with a fleet of sixty-eight vessels attacked the Genoese. The fleet of the latter, numbering seventy ships, was at Chalcedon, and tried to intercept the enemy when they endeavoured to make their way to the Golden Horn. In a battle which was fought at the mouth of the Bosporus while a strong south wind was blowing with a heavy sea--a battle which continued all night--both sides lost heavily. Eighteen Genoese ships were sunk. Pisani withdrew to Therapia, with a loss of sixteen ships. Galata, held by the Genoese, was not attacked, on account of the prevalence of Black Death,[61] or possibly because he heard that seventy or eighty other galleys were on their way to aid the Genoese. Immediately afterwards the Genoese joined with the Turks, and transported across the Bosporus a body of them to attack Constantinople. Cantacuzenus, in consequence, was obliged to make peace with his rivals in Galata by allowing them to include a large portion of additional territory within new walls,[62] as well as to take possession of Selymbria and Heraclia in Thrace. The Genoese thereupon once more became his allies. Orchan was ready to assist him, and again promised to send twenty thousand Turks to resist the party of John.