The Roman equivalent of the A1 was built to a very high standard, during the early years of Roman rule in Britain. The English successors of the Romans in Britain, called this road Ermine Street from their word for "soldier", compare the German personal name, Herman.(8a) The twenty kilometre length of Ermine Street, at roughly the centre of which, the line of the A151 lies, passed over chalky till (boulder clay) which is very sticky when wet. As the Ermine Street carriageway broke up, people sought easier going by moving down towards the small River Witham whose valley had been eroded through the till, into the Jurassic limestone below it.