Germanic tribe of the North Sea coast (roughly modern Friesland), described by Roman writers as living on artificial dwelling-mounds (terpen); alternately a Roman client people and a rebel against Roman taxation (notably the revolt of 28 CE).
Roman sources record the Frisii vanishing from the historical record after a 3rd-century crisis (flooding and Roman withdrawal from the region, c. 296 CE); the name resurfaces later for the distinct early-medieval Frisian kingdom/peoples, treated as a separate successor identity.
Primary Roman-era ethnographic source describing the Frisii and neighboring Germanic peoples of the North Sea coast.