Battle of Settepozzi The Battle of Settepozzi was fought sometime in May – July 1263 off Settepozzi ( the Italian name for Spetses ) between a Genoese - Byzantine fleet and a smaller Venetian fleet . The resulting Venetian victory had important political repercussions , as the Byzantines distanced themselves from their alliance with Genoa and restored their relations with Venice . Background . In early July 1261 , the Nicaean emperor Michael VIII Palaiologos ( r . 1259 – 1261 ) had allied himself with the Genoese in the Treaty of Nymphaeum . This alliance , whose terms were very advantageous to Genoa , was necessary for the Nicaeans and their aim of successfully recovering Constantinople , the seat of the moribund Latin Empire . The Latin emperors were backed by the naval might of Venice ( with whom Genoa was already at war ) , and without a strong navy to counter it , the city would not fall , as two previous attempts in 1235 and 1260 had demonstrated . In the event , the city was recovered by Alexios Strategopoulos barely a fortnight after the treaty was signed , without the need for Genoese naval aid . For a year thereafter , both Venice and Genoa remained rather passive . Venice hesitated to confront the numerically far superior fleet that Genoa had dispatched in the Aegean and awaited political developments in the West , while Genoa suffered from internal turmoil with the deposition of the autocratic " Captain of the People " Marino Boccanegra and the assumption of power by a collective leadership from among the noble houses . In summer 1262 , the Venetians ordered a 37 - galley fleet into the Aegean , which met the Genoese fleet of 60 ships at Thessalonica , but the Genoese refused to engage . A piratical foray , however , by the nobles of Negroponte , allied with Venice , into the Marmara Sea was confronted and defeated by a Byzantine - Genoese squadron . Battle . Meanwhile , hostilities broke out in the Morea , where Michael VIII dispatched an expeditionary force ( in late 1262 or early 1263 ) against the Principality of Achaea . Despite initial successes , Byzantine attempts to conquer the entirety of the principality were decisively defeated at Prinitza and Makryplagi . In May – June 1263 , a Byzantine - Genoese fleet of 38 or 39 galleys and 10 light cutters ( " saettie " ) , sailing to the Byzantine fortress and naval base of Monemvasia in the southeastern Morea , encountered a Venetian fleet of 32 galleys sailing north to Negroponte . The details of the engagement are not clear . The Genoese " Annales Ianuenses " claims that when the signal to attack was given , only fourteen Genoese ships advanced , while the rest stood back and then suddenly fled . The Venetian chronicler Canale , however , records that the Venetian ships attacked first , while the Genoese were trying to ambush them . The battle ended in a clear Venetian victory : the Genoese fleet , half of which failed to engage at all , lost many men , including an admiral and two of their flagships , before breaking off and fleeing . Canale claimed 1 , 000 Genoese losses as compared to 420 Venetian casualties . At any rate , the outcome was clearly the result of both the divided command of the Genoese fleet , and the reluctance , consistently displayed in earlier and later engagements , of the Genoese admirals to risk their ships : this was because the Genoese ships were fitted by private contractors , usually the rich noble merchants who ran the city , and thus constituted valuable assets for which the admirals were answerable . Repercussions . Although most of the Genoese fleet survived the battle , their defeat had major political ramifications , as Michael VIII began to reconsider the alliance with Genoa , which was very costly but had so far brought little in return , chiefly due to the Genoese admirals ' timidity . As a sign of his dissatisfaction , soon after the battle Michael VIII dismissed sixty Genoese ships from his service . The Byzantine - Genoese rift widened further in 1264 , when the Genoese " podestà " in Constantinople was implicated in a plot to surrender the city to Manfred of Sicily , whereupon the emperor expelled the Genoese from the city . Michael signed a treaty with the Venetians on June 18 , 1265 , but it was not ratified by the Doge . In the face of the threat from Charles of Anjou after 1266 , Michael was forced to renew his alliance with Genoa , but also maintained his détente with Venice , signing a five - year non - aggression pact in June 1268 .