|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 the 16th century, during the French Wars of Religion, the island became alternatively Catholic and Protestant. 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 the 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.
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, as well as the construction of Fort Boyard in the middle of the strait between Oleron and Rochefort.
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 British Navy blocus 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 the HMS Bellerophon, which took him to Plymouth before transferring him to Saint Helena.