The South or Saint Martin Island is separated from the coast of cape Centolo (monte Ferro) by a strait known as Freu da Porta. The passenger boat doesn’t reach this island. Even though the Suebi invasions were well-known in those waters, there are no remains from that period. During the 6th century, with the increment of religious orders in the Middle Ages, two hermitage-convents were built in the Cíes Islands: San Martiño in the South Island and Santo Estevo in the Middle Island. This archipelago was the object of several fortification plans during the 19th century, which resulted in the creation of an artillery warehouse in 1810 in the former monastery of Santo Estevo and a police station and a prison close to the beach of Nosa Señora. These buildings secured the place which meant an increment of the population and the installation of new activities, this resulted in the creation of the mills and other constructions like salt factories.