"x."The Piast Concept, of which the chief proponent was Jan Ludwik Popławski (late 19th century), was based on the claim that the Piast homeland was inhabited by so-called "native" aboriginal Slavs and Slavonic Poles since time immemorial and only later was "infiltrated" by "alien" Celts, Germanic peoples, and others. After 1945, the so-called "autochthonous" or "aboriginal" school of Polish prehistory received official backing and a considerable degree of popular support in Poland. According to this view, the Lusatian Culture, which flourished between the Oder and the Vistula in the early Iron Age, was said to be Slavonic; all non-Slavonic tribes and peoples recorded in the area at various points in ancient times were dismissed as "migrants" and "visitors". In contrast, the critics of this theory, such as Marija Gimbutas, regarded it as an unproved hypotheses and for them the date and origin of the westward migration of the Slavs were largely uncharted; the Slavonic connections of the Lusatian Culture were entirely imaginary; and the presence of an ethnically mixed and constantly changing collection of peoples on the North European Plain was taken for granted.