Île de la Cité
Lutetia developed on the left bank of the Seine during Roman times, and to a lesser extent on the Île de la Cité. The right bank was largely uninhabitable due to marshes. During the first barbarian invasions in AD 285, the people of Lutetia abandoned the left bank, taking refuge on the Île de la Cité and destroying the bridges. The eastern half of the island was protected by a wall, constructed of rocks collected from the Arènes de Lutèce.