In October 1352, during the Byzantine civil war of 1352–1357, John V Palaiologos, with military support from Serbia commanded by Gradislav Borilović, engaged John VI Kantakouzenos (with backing from Orhan I, the Ottoman bey). The two armies met in an open field close to the fortress walls. The more numerous Ottomans defeated the Serbs, and Kantakouzenos retained the power, while Palaiologos fled to Venetian-controlled Tenedos. According to Kantakouzenos about 7,000 Serbs fell at the battle (deemed exaggerated), while Nikephoros Gregoras (1295–1360) gave the number as 4,000. The battle was the first major engagement of the Ottomans on European soil, and made Stefan Dušan realize the major growing threat of the Ottomans to Eastern Europe. By 1361, the fortress had fallen to the Ottomans.