The mighty city walls, (on average 5 m in thickness and about 7 m in height), of the city of Posidonia / Paestum is one of the best preserved of the entire Magna Graecia; about 4,750 meters long, there are 28 towers, 4 main access doors, (Porta Marina, Porta Aurea, Porta Sirena, Porta Giustizia), 47 small openings useful for organizing the sorties during a siege. The ancient moat is currently occupied by the road that develops all around the perimeter of the walls.