Celebrated by Alexandre Dumas and his character Edmond Dantes, the Count of Monte Cristo, the Château dIf is one of the most visited sites in Marseilles, with more than 100,000 visitors a year. The island is part of the Frioul archipelago, overlooking the central harbour.
Each of the four archipelago islands has a military fort with batteries, trenches, and observation posts. Commissioned by King François I, the Château dIf and fortifications were built between 1527 and 1529, becoming the first royal fortress of Marseilles. A square building on three floors, flanked by three towers, each pierced with wide doorways, it has served mainly as a prison, escapes being impossible given the high walls with artillery platforms overlooking the cliffs.
The military architect Vauban made changes in 1702 by adding a guardhouse. The site was named a historical monument in 1926.