Based mainly on the correspondence between the local religious and secular authorities, the Sacred Congregation for the Propagation of the Faith (Propaganda Fide) in Rome, representatives of the French and Austrian governments and the Greek insurgents, this article demonstrates how the story of the Catholic community of Syros describes the making of a new frontier but also the shaping of a new territorial conception of sovereignty where multiple agents and jurisdictions co-existed next to each other for centuries. The so-called “Pope’s Island” was the only one with a solid Roman Catholic majority among its inhabitants. After the outbreak of the Greek revolt, Syros declared its neutrality and became a safe haven for Orthodox refugees fleeing from Ottoman reprisals, especially after the Chios massacres in April 1822. By 1825, around 30,000 (mainly Orthodox) refugees had taken over the port, which in the meantime became a Christian “Eldorado” of legal trade and illegal traffic of all sorts, including piracy booties and slave labour.