The ancient city of Lincoln, the Roman Lindum, was divided into two parts, the upper and the lower. The upper consisted of a nearly rectangular area, roughly 500 yards from east to west by 418 yards from north to south, surrounded by massive walls 10 to 12 feet thick, and further strengthened by an enormous fosse. It lay with its longer side upon the edge of a table-land which sloped rapidly down to the wide valley formed by the river Witham.