The history of Petrovac began in Roman times, when a couple of villas were built at Krš Medinski: a 4th-century mosaic floor, remains of a villa and baths have been found behind St Ilija's church. Later, there was a Slav village. The village was first mentioned in the Chronicle of the Priest of Duklja. At the northern end of the bay is a 16th-century Venetian fortress, Kastel Lastva, built to discourage pirates. When in the late 16th century jurisdiction of the Benedictine monastery Ratac collapses the Orthodox rite began to strengthen in the area of Catholic parishes, Spič, Sozina and Kastel Lastva which were under jurisdiction of this monastery. The Orthodox clergy and the Orthodox believers at the same time began to use Catholic Churches of that area for their rites. The name, Petrovac, was given at the beginning of the 20th century after King Peter I Karađorđević. Before, the name was Kaštel Lastva.