This paper addresses the reorganisation of Ottoman military organisation and resources in the hinterland of Euboea and Lepanto in the face of the gradual change of power balance in the eastern Mediterranean in the second half of the fifteenth century, and examines to what extent the Ottoman coastal defence capabilities were improved by the 1520s. The tahrir defters of Tırhala Sancağı (pre-1440, 1454/1455, 1466/1467, 1480, 1506, 1521) and those of Eğriboz Sancağı (1474, 1506, 1521) not only show that the nahiyes of Vodonitsa, İstefe and Livadiye under Tırhala Sancağı since the mid-fifteenth century were attached to Eğriboz around 1507, but also cast light on the gap between the resource and military potential of provincial troops in the two sancaks. The timar system had been well implemented in Tırhala no later than the 1440s, and the late fifteenth century witnessed a significant increase in ordinary timariots’ average annual revenue (3266.57 akçe in 1454/1455 to 5993.43 in 1480) along with the prebend holders’ growing capability to finance more armed retainers in Tırhala. In contrast, in 1474, many timars in newly-conquered Eğriboz were still noted as ‘reserved’ (mevkuf). Textual sources, such as petitions and investigation reports, also exhibit the Eğriboz military-administrative officials’ desperate need for additional revenue income and manpower to deal with fortress renovation and frequent piracy. The increased demand for financial and human resources from the Euboean side led to the contests and disputes over taxation during harvest season between the timariots in İstefe and the Eğriboz sancakbeyi, as seen in the 1500/1501 ahkâm defteri. The paper argues that the Porte attached Vodonitsa, İstefe and Livadiye to Eğriboz Sancağı around 1507 in the hope that this sea border sub-province could get more manpower and financial resources for coastal defence, heralding the establishment of the Eyalet of Archipelago (1534). The 1521 Eğriboz tahrir defteri proves that these three nahiyes contributed 48.5% of the total revenue from the prebends in Eğriboz that year, supplying 5 of the 8 zeamets under Eğriboz. Thanks to these additional resources, the local governors might have been enabled to strengthen the castles and garrisons. Military mobilisation reports from the 1520s demonstrate that a secured Euboean coastline was complementary to the vital transportation of Thessalian grains from the Euboean Gulf to the rest of the empire, and the deployment of the Thessalian provincial troops who were often summoned to join the imperial expeditionary armies elsewhere.