The history of the Old Fortress dates back to the mid-6th century AD when the ancient city of Corfu on the Kanoni Peninsula (Chersoupolis, modern-day Palaiopolis) was destroyed in barbarian incursions. It was then that its inhabitants began gradually moving to the naturally fortified peninsula of the Old Fortress with its two peaks, where the Byzantine city, Koryfo (from which the island took its name Corfu) developed. The Byzantines and later the Angevins (1267-1386) walled the peninsula and built towers on both its peaks.
The current form of the Old Fortress?s fortifications is mostly owed to the defensive works done during the period of the Venetian rule (1386-1797). The Venetians took care to secure possession of Corfu due to its strategic and commercial importance. This was why they modernized the Fortress?s defensive works to withstand Ottoman attacks. The form these works assumed was dictated by the new development brought about by the introduction of heavy artillery into the art of war. Initially, the peninsula was separated from the island itself through the construction of the sea moat, the so-called contrafossa. For defensive reasons, a zone that remained unbuilt was simultaneously created between the Fortress and the settlement developed outside the walls (xopoli or borgo), the spianata, modern-day Spianada.
Following the destructive Turkish siege of 1537, the Venetians once again modernized Koryfo?s fortifications. The great Veronese architect Michele Sanmicheli and his nephew Gian Gerolamo Sanmicheli gave the fort its characteristic form following the principals of the bastian system (fronte bastionato). Their major projects included the west front with the two pentagonal bastions, the intervening wall, and the entrance which opens in the center of the wall. The land connection was achieved by a movable bridge. A short time later (second half of the 16th c.), Cape Kavosidero at the northeast end of the peninsula was also walled. When the capital was transferred to the Xopoli in the late 16th century, Koryfo remained primarily a military base.
During the period of English rule (1814-1864), large-scale interventions were made at the site of the Old Fortress with the construction of new buildings, chiefly military. During World War II, bombing destroyed important Venetian buildings such as the palace of the Proveditore (Governor) and the Pasqualigo?s Barracks.
Today the Old Fortress, the New Fortress, the Old City of Corfu together with the rest of the fortifications of the city are UNESCO World Heritage Monuments.