The site of Aigues-Mortes (the name translates to "Dead Water") was already of interest in the Roman era: Located in the Camargues, the estuary of the Rhône river, it was used a saline since the Neolithic era. Legend says that the first settlement was founded in 102 BC by the Romans, but there is no surviving evidence of that claim. Carolus Magnus erected the first fortifications in the location in the 8th centuries which survive until today.

The settlement was heavily fortified in the 13th century when the French kings wanted a Mediterranean port under their direct control. As such Aigues-Mortes became the starting point of crusades under French leadership. The walls of the city were constructed at the same time.

Due to the shift of the marshland around it, Aigues-Mortes lost and regained its access to the sea several times. Nonetheless it lost its strategic importance when the French kings gained direct control of the Provence and thus could make use of the much bigger ports of Marseille and Toulon. The town survived due to the salines in its vicinity and remained largely unchanged for centuries.