The decline of Celtic power under the expansive pressure of Germanic tribes (originally from Scandinavia and Lower Germany) and the forming of the Roman Empire during the 1st century BC was also that of the end of prehistory, properly speaking; though many regions of Europe remained illiterate and therefore outside written history for many centuries, the boundary must be placed somewhere, and that date, near the start of the calendar, seems to be quite convenient. The remaining is regional prehistory, or, in most cases, protohistory, but no longer European prehistory, as a whole.