During the Roman period, it seems the island was connected to the continent at low tide. She finally took her current shape around 1500.
At the end of the 12th century, France and England fought for the possession of the 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 about 15 years.
In 1665, the nearby Rochefort was established as a strategic harbour for the Kingdom, prompting many fortification to be built in the area. Vauban built numerous fortifications on the island, which were completed in 1704 by Ferry.
During the Seven Years' War (1756–1763) the English captured the island and destroyed its ramparts. The fortifications were then rebuilt by several French officers, including Pierre Choderlos de Laclos, the author of Les Liaisons dangereuses.
Napoleon famously visited the island in 1808 and gave directions to reinforce the fortifications. He ordered the construction of a house for the commander of the stronghold (today's "Musee Napoleon"), and the construction of Fort Liedot, named after a colonel killed in the Russian campaign.
In 1815, from July 12th to 15th, Napoleon also spent his last days in France at Ile d'Aix, after the defeat at Waterloo, in an attempt to force a Royal Navy blockade to escape to the United States. Realizing the impossibility to accomplish this plan, he wrote a letter to the British regent. and finally surrendered to HMS Bellerophon, which took him to Plymouth before transferring him to Saint Helena.
Access to the island is provided by a ferry that leaves several times a day year round from Fouras just east of the island, or from La Rochelle, and Oléron, during the summer months. Cars (except for service vehicles) are prohibited on the island, affording more tranquility. People move around on foot or by bicycle. Horse carriages are also available to circle the island.