The town known as «Portus Veneris» was already famous for its beauty in Roman times. The ancient nucleus developed around the modern-day promontory of San Pietro, where there was a temple dedicated to Venus Ericina, which is where the town's name derives from. A Byzantine stronghold in mediaeval times, it was destroyed by the Rotari in 643 AD but grew again over the next centuries thanks to the monastic movement, which involved the two islands of Palmaria and Tino. It was conceded by the Da Vezzano family in 1113 to the Genoese, who developed the military and marine potential of the town by building the characteristic row of fort-houses along the coast, the walls, the three towers, the town gate and, between 1118 and 1130, the church of San Lorenzo, which was the work of the Antelami master builders. Portovenere was an unconquerable bastion of the Republic of Genoa during the long war against Pisa: the characteristic church of San Pietro on the clifftop was built by the Genoese in 1256, as a token of gratitude for the decisive contribution of the local inhabitants in the conquest of Lerici. The «upper castle» was built by the Byzantines and resisted two Pisan sieges in 1165 and 1198; it was demolished in the fifteenth century to make room for the fortress, which was constructed in a number of phases until 1751. It is today open to visitors and used as an exhibition space for shows and cultural events. A road leading out of Portovenere takes you up the steep hillside towards the Cinque Terre through the Mediterranean maquis. You can also reach the Muzzerone free-climbing area from here. A boat service takes visitors to the island of Palmaria, which is a regional park: protected from building speculation, it offers tourists beaches, cliffs, natural vegetation and grottoes that can only be reached by boat. The «grotta dei colombi» was a prehistoric dwelling. The island of Tino lies beyond Palmaria: it is a military zone and is only open to visitors once a year on the occasion of the feast of San Venerio, the hermit who lived on the island in the tenth century.