In 52 BC, at the time of Vercingetorix's struggle with Julius Caesar, a small Celtic tribe, the Parisii, lived on the island, which was a low-lying ait subject to flooding that offered a convenient place to cross the Seine and a refuge in times of invasion. Here Saint Genevieve led the local people for defense, and here Clovis established a Merovingian capital.
Three medieval buildings remain on the Ile de la Cité:
The Cathedral of Notre-Dame de Paris, built from 1163 on the site of a church dedicated to Saint Etienne, which in turn occupied a sacred pagan site of Roman times. During the French Revolution the cathedral was badly damaged, then restored by Viollet-le-Duc. A plaque in the square in front (Place du Parvis de Notre-Dame) is the zeropoint for measurements "from Paris."
Louis IX's Sainte-Chapelle (1245), built as a reliquary to house the relics of the Crown of Thorns and a piece of the True Cross, enclosed within the Palais de Justice.
The Conciergerie prison, where Louis XVI and Marie Antoinette awaited execution in 1793.
The oldest remaining residential quarter is the "Ancien Cloitre". Baron Haussmann demolished some streets here, but was dismissed in 1869, before the entire quarter was lost.
The small park at the downstream tip, the "stern" of the island-ship, is "Vert Galant" park, named for Henri IV of France, the "Green Gallant" king. It shows the original low-lying riverside level of the island. Nearby, a discreet plaque commemorates the spot where Jacques de Molay, Grand Master of the Knights Templar, was burnt at the stake, March 18, 1314.
The Ile de la Cité is connected to the rest of Paris by bridges to both banks of the river and to the Ile Saint-Louis. The oldest surviving bridge is the Pont Neuf ('New Bridge'). It has one station on the Paris Metro, "Cité", and the RER station "Saint-Michel-Notre-Dame" on the south bank has an exit on the island in front of the cathedral.