Friso-Saxon is a collective name for a certain group of dialects belonging to the West Germanic languages. Although they are a variant of the Low Saxon language as a whole, these dialects have undergone strong influences from the Frisian language. Most of the Friso-Saxon dialects were Frisian dialects themselves in the past, until Frisian was replaced with Low Saxon in the Late Middle Ages. However, Frisian has remained a substratum since then in the regions concerned. The only exception to this rule is Stellingwarfs, a Low Saxon dialect which has undergone influence especially from West Frisian. Most of the other Friso-Saxon dialects underwent most influence from East Frisian, for example East Frisian Low Saxon, while the dialect of Dithmarschen which underwent most influence from North Frisian.