These were shipowners who, in 1664, wished to fortify the area and build a watchtower that would be visible 20 km from Marseille's harbour to facilitate the work of commercial ships.
It is called the Tour du Fanal or Tour Ronde. Fort Saint Jean was built under Louis XIV's orders from 1668 to 1671 after the expulsion of the Hospitallers. In 1679, after a rebellion by the inhabitants of Marseille, it was separated from the rest of the city with the digging of a ditch by Vauban.
The complex retained a military vocation until the revolution, before becoming a state prison. During World War II, the fort used to be an ammunition depot for the Germans was heavily damaged by an accidental explosion
