The origins of the small ancient town of Les Mureaux and its port lie in a grouped settlement established during the La Tene C1 period on a boundary island of the territory of the Carnutes at the crossroads of the Seine river and an overland route connecting Orléans (Loire) to Beauvais (Oise). The earliest traces of a river port established on a second island, located between a dead arm of the river and an active channel, are dated to the beginning of the 1^st c. AD on the site of a former residential area. In the mid-1^st c. AD the port was developed to include a series of adjoining terraces maintained by drystone retaining walls, along with quays and basins. This development covered the entire island on either side of the cardo maximus of the city and its bridge. Mooring places are indicated by masonry pilings in the dried-up streambed. The site was gradually abandoned from the end of the 1^st c. AD on and definitely in the mid-2^nd c. AD when the dead arm of the river was backfilled. The abandonment of the port seems to be part of a general decline of the small town. The river banks were only gradually occupied again from the 5^th c. AD onwards.