Old Navarino fortification (Palaiokastro) is located on the promontory supervising the naturally endowed Navarino-bay at the south-western foot of Peloponnese peninsula, near the contemporary city of Pylos. The cliff where it is built and where ancient relics lie, was fortified by Frankish in the thirteenth century. The fortification though knows significant alterations firstly by Serenissima Republic of Venice from the fifteenth century that aims to dominate the naval routes of Eastern Mediterranean by establishing a system of coastal fortifications and later by the Ottomans after the conquest of Venice’s possessions at Messenia in 1500. Between fifteenth and seventeenth century, apart from important modifications at the initial enceinte of the northern Upper City, the most notable transformation of Old Navarino is the construction of the new Lower fortification area at the south and the southern outwork ending up to the coastline. Especially the Lower fortification is a sample of multiple and large-scale successive alterations for the adjustment to technological advances of artillery (fortification walls reinforcement, modification of tower-bastions, early casemates, gate complex enforcements). The current essay focuses on the study of these specific elements of the early artillery period and the examination of Old Navarino’s strategic role at the time of transition before the adaptation of “bastion-front” fortification patterns, such as those experimented in the design of the fortified city of New Navarino, constructed at the opposite side of the Navarino gulf by the Ottomans (1573).