A for­ti­fi­ca­tion on the island of If in the Frioul arch­i­pel­ago in the Mediter­ranean Sea. Ini­tial­ly, the struc­ture was built as a fort to defend Mar­seille from attacks from the sea. Con­struc­tion took place in 1524–1531 by order of King Fran­cis I. From the end of the 16th cen­tu­ry, the cas­tle began to be used to iso­late and guard espe­cial­ly dan­ger­ous crim­i­nals. The dun­geons con­tained Huguenots, politi­cians, lead­ers of the Paris Com­mune, and per­sons who posed a dan­ger to France.

In the 1830s, the Château d’If offi­cial­ly ceased to be a prison, but in 1871, the lead­ers of the Paris Com­mune were held here, and its leader Gas­ton Crémieux was shot on the island of If. In the 19th cen­tu­ry, the cas­tle was turned into a muse­um, and in 1926 it was giv­en the sta­tus of an archi­tec­tur­al mon­u­ment.

The cas­tle gained wide fame thanks to the French writer Alexan­dre Dumas. In his nov­el The Count of Monte Cristo, writ­ten in 1844–45, the pro­tag­o­nist, Edmond Dantes, was impris­oned in the Chateau d’If.