During the Huguenot Rebellions of the 1620s, Cardinal Richelieu ordered that the island be fortified as a counterweight to the nearby Protestant city of La Rochelle on the French mainland.

After La Rochelle had been subdued, Saint-Martin's fortifications were largely demolished to remove its potential threat to royal power.

In 1627, an English invasion force under the command of George Villiers, Duke of Buckingham attacked the island in order to relieve the Siege of La Rochelle.

Later, in the 1670s, the French engineer, Vauban was commissioned to review and overhaul the island's defences and, as a result, Saint Martin was enclosed by extensive and modern walls and embankments.

This was done in three major phases ending in 1702 and the result was an enclosed town capable of housing the island's population for a long siege.