This website says:

“The oldest population of Paris used to live on the city island. It was a Celtic population. They were called the Parisii. They arrived three centuries before Christ and settled on the island because they were protected by the water all around. The word Parisii means « sailor » in Celtic language. Then the roman people (coming from the actual Italy) invaded Paris (then called Lutetia) by the south and settled down on the left bank of the seine river.”

Another says largely the same:

“Paris was founded in the 3rd century B.C. on île de la Cité by a community of Celts. They were a group of tribal fishermen called the Parisii who, pushed by emigration towards the banks of the Seine, made a permanent settlement there and profited from the area’s fertility and temperate climate.”