The Romans then began a night march to escape, but marched into another trap that Arminius had set, at the foot of a hill near Osnabrück. There, the sandy, open strip on which the Romans could march easily narrowed at the bottom of the hill. There was a gap of only about 100 m between the woods and the swampland at the edge of the Great Bog. The road was blocked by a trench, and, towards the forest, an earthen wall had been built along the roadside. This let the tribesmen to attack the Romans from cover.