This paper addresses the problem of the Greek-Latin frontier in the Peloponnesos in the second half of the thirteenth century. In 1262, Byzantium regained control over a part of the peninsula. This action disrupted the order that developed there during fifty years and changed the power balance in the region. The author has analysed the transformation of the frontier society of the Peloponnesos when Byzantine administration returned to the country and the peculiarities of integration processes and socio-cultural interethnic interaction under the changed political realities. The sources for the research were the Chronicle of Morea and Latin and Byzantine legislative sources. It has been revealed that in the early years of the “Byzantine reconquest,” the struggle between the Byzantines and the Franks for the territories was accompanied by their rivalry for the political loyalty of the local population. Although the Byzantine strategy of encouraging the Greek resettlement from the Frankish regions to the regions of Mistra had some impact, these migrations did not become widespread; neither did complete isolation of the Greek population from the Latin occur. In the conditions of intensive socio-cultural exchange, the political loyalty of the mixed population of the peninsula was determined either by personal motives or by the wish to have protection, which was especially important in time of military operations. Despite frequent military conflicts, the mixed Greco-Latin society continued to exist and develop, and the persons living in changing political and cultural realities often had to manoeuvre between the Franks and the Byzantines. The conclusion is that the Byzantine restoration in the Peloponnesos did not interrupt the integration processes, and the frontier society kept its special and complex way of life that shaped on the border of the Latin and Byzantine civilizations.