Best known as the setting for Dumas' 1844 classic novel on revenge, there's a great deal more of significance here to those who love church history. Calvin dedicated his theological classic, The Institutes of the Christian Religion (1536) to King François I, and it was that same king who ordering the building of D'If (1529) as a royal fort to protect his war galleys anchored in Marseille.
In the Huguenot wars beginning in 1562, D'If became a royal prison. Among with the mainland fortress overlooking the city, 3,500 Huguenots were held in the dungeons of this impregnable fortress. When Henry of Navarre was crowned Henry IV of France, staunchly Roman Catholic Marseille refused to acknowledge a one-time Huguenot as their king. Enclosure fortification raised to further resist Henry were destroyed by the king.
Another less important though interesting fact about Chateau D'If: The rhinoceros Protestant German artist Albrecht Dürer used for his famous woodcut (1513) made a stopover at the chateau on its way as a gift to Pope Leo X, chief nemesis of Martin Luther.
All that said, we had glorious weather for our great visit to the island fortress, Giles and Gillian running around like crazy children from the middle ages thoroughly enjoying the fortress and the rocky seaside, with water so clear you can see every detail on the bottom.