 Before the 19th century, scholars assumed that the original land of the Celts was west of the Rhine, more precisely in Gaul, because it was where Greek and Roman ancient sources, namely Caesar, located the Celts.This view was challenged by the 19th-century historian Marie Henri d'Arbois de Jubainville who placed the land of origin of the Celts east of the Rhine.Jubainville based his arguments on a phrase of Herodotus' that placed the Celts at the source of the Danube, and argued that Herodotus had meant to place the Celtic homeland in southern Germany.