Map of the "Lutetian Campaign" from Napoleon III's book about Caesar. It presents the most commonly accepted theory. Nevertheless, the traditional location of the Gallic oppidum is now much debated.
  The battle of Lutetia

In 53 BCE, Lutetia is mentioned for the first time in Caesar's Gallic Wars as the place where Caesar called a meeting of the Gallic tribes in the territory of the Parisii. We are given more precise information, however, with the famous episode of the "Battle of Lutetia" in 52 BCE:
While Caesar is facing difficultes at Gergovia, son his lieutenant Labenius leaves Agedincum with four legions to go to « Lutetia, oppidum of the Parisii located on an island in the Seine » to fight a coalition of the Parisii and other tribes led by the aged chief Camulogenus. In order to block the legions' path, the chief establishes camp « in a continuous marsh leading to the Seine ». Labenius attempts to cross it but gives up in the face of the difficulties encountered. Retracing his steps, he takes Melun by surprise. He then moves his legions to the other shore and heads for Lutetia along the river. Warned of this manoeuvre, the Gauls burn Lutetia and cut the bridges. Camulogenus leaves the marsh nd sets up on the banks of the Seine facing Lutetia and watches Labenius's camp from the other shore. Labenius outsmarts him by crossing the river by boat our Roman miles (about 16 kilometres) upstream. The two armies are now face to face on the same side of the river. The battle begins and the Romans are victorious.