During the Roman period, it seems the island was connected to the continent at low tide.
It finally took its current shape around 1500.
In 1067, Isembert de Châtelaillon gave the island to the order of Cluny.
A small convent was established, which depended on St Martin, on Île de Ré.
At the end of the 12th century, France and England fought for the possession of Aix island.
Until 1286, the island was located at the boundary between the French and the English Saintonge,
formed by the estuary of the Charente River. During the Hundred years war, Aix became English for 15 years.
In the 16th century, during the French Wars of Religion, the island became Catholic and then Protestant.
In 1665, nearby Rochefort was established as a strategic harbour for the Kingdom, leading to
the construction of many fortifications in the area.
During the Seven Years' War (1756–1763) the British captured the island in 1757 and destroyed
its ramparts as part of the attempted Raid on Rochefort, before withdrawing several weeks later.
The island of Île d'Aix was again captured by British forces in 1759 following the Battle of Quiberon Bay,
and occupied until the end of the war in 1763. The fortifications were then rebuilt by several
French officers, including Pierre Choderlos de Laclos, the author of "Les Liaisons dangereuses".
During the French revolution, in 1794, the island was used as a prison for the suppression
of religious opponents, in which hundreds of priests were left to die in moored prison-boats.