In his account of the Gallic wars, Julius Caesar addresses an assembly of leaders of the Gauls in Lucotecia, asking for their support. Wary of the Romans, the Parisii listened politely to Caesar, offered to provide some cavalry, but formed a secret alliance with the other Gallic tribes, under the leadership of Vercingetorix, and launched an uprising against the Romans in January 52 BCE.

One year later, the Parisii are defeated by the Roman general Titus Labienus at the Battle of Lutetia. A Gallo-Roman garrison town, called Lutetia, is founded on the left bank of the Seine. The Romans built an entirely new city as a base for their soldiers and the Gallic auxiliaries intended to keep an eye on the rebellious province. The new city was called Lutetia or "Lutetia Parisiorum" ("Lutèce of the Parisii"). The name probably came from the Latin word luta, meaning mud or swamp Caesar had described the great marsh, or marais, along the right bank of the Seine. The major part of the city was on the left bank of the Seine, which was higher and less prone to flood. It was laid out following the traditional Roman town design along a north–south axis.

On the left bank, the main Roman street followed the route of the modern day Rue Saint-Jacques. It crossed the Seine and traversed the Île de la Cité on two wooden bridges: the "Petit Pont" and the "Grand Pont" (today's Pont Notre-Dame). The port of the city, where the boats docked, was located on the island where the parvis of Notre Dame is today. On the right bank, it followed the modern Rue Saint-Martin. On the left bank, the cardo was crossed by a less-important east–west decumanus, today's Rue Cujas, Rue Soufflot and Rue des Écoles.