The Old Fortress occupies the rocky eastern end of Corfu town, a naturally defensible promontory separated from the later city by a moat known as the Contrafossa. Byzantine communities fortified the two peaks after insecurity encouraged settlement away from the older town of Paleopolis. The twin heights gave the place its medieval name, Korypho, often linked to the modern name Corfu. Walls, towers, gates, cisterns, churches, dwellings, and military stores developed over centuries rather than in one campaign.

Venice took control of Corfu in 1386 and transformed the fortress as artillery changed Mediterranean warfare. Engineers strengthened bastions, cut the moat, reshaped approaches, and created layers of defense commanding the harbor and sea routes between Italy and the eastern Mediterranean. The island remained Venetian until 1797 and resisted repeated Ottoman attacks, including major sieges in 1537 and 1716. Soldiers and sailors depended on civilians, laborers, artisans, water systems, magazines, and maritime supply during both siege and ordinary garrison life.

French, Russo-Ottoman, and British administrations followed the end of Venetian rule. The British governed the Ionian Islands from 1815 until union with Greece in 1864 and altered the fortress for modern military use. They built the neoclassical Church of Saint George, whose temple-like form differs from the older Venetian works, as well as barracks and service buildings. Explosions, demolition, earthquakes, weather, and Second World War bombing damaged or removed other structures, producing the complex mixture visible today.

The fortress later became a monument and cultural venue while retaining military and administrative associations. Visitors cross the Contrafossa and pass through successive works before reaching elevated viewpoints over Corfu town and the Ionian Sea. Museums, archives, exhibitions, concerts, and public offices have occupied parts of the site. Surviving masonry includes different periods of construction and repair, so labels and conservation records are necessary to distinguish Byzantine origins, Venetian engineering, British additions, Greek adaptations, and modern restoration.

The Old Fortress is significant as the defensive nucleus from which Corfu town developed and as evidence of competition for a strategic island. It belongs to the historic urban landscape recognized by UNESCO, but its meaning extends beyond picturesque walls. Interpretation should include siege, civilian displacement, religious change, military labor, and the practical systems that kept a crowded citadel functioning. Conservation must manage salt, wind, vegetation, drainage, unstable rock, and heavy visitation. The fort's layered fabric demonstrates that Mediterranean strongholds were continually rebuilt as governments and technologies changed.