The Amisius flowed from the Teutoburg Forest, home of the Cherusci, with the Bructeri and others bordering the river. These tribes were among the initial Franks. The Romans were quite interested in adding them to the empire, and to that end built a fort, Amisia, at the mouth of the Ems. As the river was navigable to their ships, they hoped to use it to access the tribes at its upper end.