The Mor|in|i = "sea people", had tribal lands centred on Therouanne, Tarouanna civitas Morinorum.

Their territory was bounded to the south be the Canche, to the south east by the territory of the Atrebates and to the northeast by the Menapii on the Aa.

Caesar tried unsuccessfully to reduce the Morini in 56 BCE but in 55 BCE they accepted the Roman alliance. It is possible that the Morini once enjoyed a much larger territory east of the Aa stretching to the north east along the coast. Certainly in the time of Caesar their neighbours, the Menapii, were on the Rhine at its mouth and the Maas.

A southward move of the Menapii might be linked to the disturbances on the Rhine caused by the Suebi in 30-29 BCE and the simutaneous revolt of the Morini put down by C Carrinas. It is likely then that the land lost by the Morini reported by Dion Cassius lay east of the Aa. The important site at Cassel became the tribal capital of the Menapii.