The entire island is heavily fortified; high ramparts with gun platforms surmount the cliffs, which rise steeply from the surrounding ocean.

It was built from 1524 to 1531 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 closest that it came to a genuine test of strength was in July 1531, when the Holy Roman Emperor Charles V made preparations to attack Marseille.

In 1701, the military engineer Vauban questioned its suitability to defend against an actual attack: "The fortifications look like the rock[;] they are fully rendered, but very roughly and carelessly, with many imperfections.

[5] The isolated location and dangerous offshore currents of the Château d'If made it an ideal escape-proof prison, very much like the island of Alcatraz in California in more recent times.

Over 3,500 Huguenots (French Calvinist Christians) were sent to Château d'If, as was Gaston Crémieux, a leader of the Paris Commune, who was shot there in 1871.

The island became internationally famous in the 19th century, when Alexandre Dumas used it as a setting for his novel The Count of Monte Cristo, published to widespread acclaim in 1844.

In the novel, the main character Edmond Dantès (a commoner who later purchases the noble title of count) and his mentor, Abbé Faria, were both imprisoned in it.