The king noted during his visit that Marseille was poorly defended. The need to reinforce its defenses became even more obvious in 1524 after constable Charles III, Duke of Bourbon and emperor Charles Quint lay siege to the city and almost took it. François I built two forts: one on the island of If, which became the famous Chateau d'If, the other at the top of La Garde, which included the chapel. This is the only known example of a military fort sharing space with a sanctuary open to the public.