Byzantine – Genoese War ( 1348 – 49 ) The Byzantine – Genoese War of 1348 – 1349 was fought over control over custom dues through the Bosphorus . The Byzantines attempted to break their dependence for food and maritime commerce on the Genoese merchants of Galata , and also to rebuild their own naval power . Their newly constructed navy however was captured by the Genoese , and a peace agreement was concluded . Background . The Genoese held the colony of Galata on the Golden Horn across from the city of Constantinople since 1261 as part of the Treaty of Nymphaeum , a trade agreement between the Byzantines and Genoese . However , the dilapidated state of the Byzantine Empire following the civil war of 1341 – 1347 was easily shown in the control of custom duties through the strategic straights of the Bosphorus . Even though Constantinople was the Imperial seat of power with its cultural and military center on the shores of the Bosphorus , only thirteen percent of custom dues passing through the strait were going to the Empire . The remaining 87 percent was collected by the Genoese from their colony of Galata . Genoa collected 200 , 000 " hyperpyra " from annual custom revenues from Galata , while Constantinople collected a mere 30 , 000 . The Byzantine navy , a notable force in the Aegean during the reign of Andronikos III Palaiologos , was completely destroyed during the civil war . Thrace , the main imperial possession and only taxable region of the Empire , was still recovering following the destruction of marauding Turkish mercenaries during the civil war . Byzantine trade was ruined and there were few other financial reserves for the Empire other than the duties and tariffs from the Bosphorus . The conflict . In order to regain control of the custom duties , the emperor John VI Kantakouzenos made preparations to lower Constantinople ' s duties and most tariffs to undercut the Genoese in Galata . Still recovering from the civil war of 1341 – 1347 , the emperor - with great difficulty , raised 50 , 000 " hyperpyra " from private sources ( as the state treasury was empty ) for a shipbuilding program for the expected war to come . When the tariffs and custom duties were finally lowered , merchant shipping coming through the strait bypassed Genoese Galata and diverted their ships across the Golden Horn to Byzantine Constantinople . The Genoese , hard hit financially from this policy , declared war on the Empire , and in August 1348 , a flotilla of ships sailed across the Horn attacked the Byzantine fleet and despite their large scale preparations , the Byzantine fleet was destroyed by early 1349 . The Byzantines retaliated by burning wharfs and warehouses along the shore and catapulted stones and burning bales of hay into Galata , setting major parts of the city on fire . After several weeks of fighting , plenipotentiaries from Genoa came and negotiated a peace agreement . The Genoese agreed to pay a war indemnity of 100 , 000 " hyperpyra " and evacuated the land behind Galata which they illegally occupied ; finally they promised never to attack Constantinople . In return the Byzantine surrendered nothing , however the Genoese custom duties remain in effect . Aftermath . The devastation of the 1341 – 1347 civil war so greatly weakened the Empire that its financial reserves were irrevocably depleted . Their only recourse was to make an attempt to take control of the custom duties and tariffs of the trade route through the Bosphorus . The 1348 - 49 war was the last attempt for the Byzantines to retake control single - handedly . From 1350 , the Byzantines allied themselves to the Republic of Venice , which was also at war with Genoa . As Galata remained defiant however , the Byzantines were forced to settle the conflict in a compromise peace in May 1352 . Thereafter , few other financial resources remained for the Empire , which contributed to their decline and final downfall in 1453 .