The Île de la Cité is the island in the River Seine at the very centre of Paris. It has been occupied for centuries, from Gallo-Roman days onwards. Excavations in the large square in front of Notre Dame Cathedral from 1965 to 1972 revealed many of the remnants of successive occupations and these have been preserved in a crypt enclosing an area of around 120 by 60 metres.
The remains are particularly rich as since the square was created by Haussmann in 1877 the area has escaped the developments that have destroyed much of the subterranean remains elsewhere in Paris. Structures that remain include a Roman bath-house with hypocaust, cellars and wells and the former Hospice for Foundlings.
The crypt opened as a museum in 1980.