The excavations began in October 2016 at the request of the French state, after local authorities bought land near the modern-day city of Uzes (near Nimes) to build a boarding school and a canteen.
In the summer of 1940, following the fall of France, the Duke and Duchess had taken refuge in Lisbon, the capital of neutral Portugal.
The archaeologists found that the site had been occupied from the 1st century BC to the late Antiquity (7th century AD), with an interruption in the 3rd and 4th century, which they haven't been able to explain.
They also identified building remains from the Middle Ages, although these were more rare.
In the process, the researchers shed a light on the mysterious past of the Roman city of Ucetia.
"Prior to our work, we knew that there had been a Roman city called Ucetia only because its name was mentioned on stela in Nimes, alongside 11 other names of Roman towns in the area.