Île d’If measures 3 hectares (0.03 km2) and is located 3.5 km (2 1⁄8 mi) west of the Old Port of Marseille. The entire island is heavily fortified; high ramparts with gun platforms surmount the cliffs that rise steeply from the surrounding ocean. Apart from the fortress, the island is uninhabited.
The "château" is a square, three-story building 28 m (92 ft) long on each side, flanked by three towers with large gun embrasures. It was built in 1524-31 on the orders of King Francis I, who, during a visit in 1516, saw the island as a strategically important location for defending the coastline from sea-based attacks.
The castle's principal military value was as a deterrent; it never had to fight off an actual attack. The closest that it came to a genuine test of strength was in July 1531, when Holy Roman Emperor Charles V made preparations to attack Marseille. However, he abandoned the invasion plan.
This might have been fortunate, given the weaknesses identified by military engineer Vauban in a scathing report in 1701: "The fortifications look like the rock, they are fully rendered, but very roughly and carelessly, with many imperfections. The whole having been very badly built and with little care... All the buildings, very crudely done, are ill made."
The embalmed body of general Jean Baptiste Kléber was repatriated to France after his assassination in Cairo in 1800. Napoleon, fearing that his tomb would become a symbol to Republicanism, ordered that the body stay at the château. It remained there for 18 years until Louis XVIII granted Kléber a proper burial in his native Strasbourg.