Wikipedia
The Chauci (, and identical or similar in other regional modern languages) were an ancient Germanic tribe living in the low-lying region between the Rivers Ems and Elbe, on both sides of the Weser and ranging as far inland as the upper Weser. Along the coast they lived on artificial hills called terpen, built high enough to remain dry during the highest tide. A dense population of Chauci lived further inland, and they are presumed to have lived in a manner similar to the lives of the other Germanic peoples of the region.
Their ultimate origins are not well understood. In the Germanic pre- Migration Period (i.e., before c. 300 AD) the Chauci and the related Frisians, Saxons, and Angles inhabited the Continental European coast from the Zuyder Zee to south Jutland. All of these peoples shared a common material culture, and so cannot be defined archaeologically. The Chauci originally centered on the Weser and Elbe, but in c. AD 58 they expanded westward to the River Ems by expelling the neighboring Ampsivarii, whereby they gained a border with the Frisians to the west. The Romans referred to the Chauci living between the Weser and Elbe as the 'Greater Chauci' and those living between the Ems and Weser as the 'Lesser Chauci'.
The Chauci entered the historical record in descriptions of them by classical Roman sources late in the 1st century BC in the context of Roman military campaigns and sea raiding. For the next 200 years the Chauci provided Roman auxiliaries through treaty obligations, but they also appear in their own right in concert with other Germanic tribes, opposing the Romans. Accounts of wars therefore mention the Chauci on both sides of the conflict, though the actions of troops under treaty obligation were separate from the policies of the tribe.
The Chauci lost their separate identity in the 3rd century when they merged with the Saxons, after which time they were considered to be Saxons. The circumstances of the merger are an unsettled issue of scholarly research.