The Old Fortress of Corfu is located at the eastern tip of the town and is one of the first characteristic landmarks that visitors see when approaching Corfu by boat. The fortress is set on a promontory that contained the small Medieval town, to protect it from the frequent invasions of the island by barbarian hordes and pirates. The original Byzantine fortifications were improved later on by the Angevins of Naples and last by the Venetians. In the early 16th century a deep moat, called the “Contra Fossa”, that includes a narrow sea-water channel, separated it from the land to the West, converting it to an artificial island. The Old fortress, together with the New Fortress built later, successfully contributed to the defense against the Ottoman sieges of the town in 1537, in 1571 and the last one in 1716.