The way the British defended themselves in Iron Age times was by building ditches and earth walls on top of hills. They are called hillforts. At a sign of trouble, a group of people would rush to their fort and seal the entrance. However, for most of the time, the hilltop area was used as a kind of king's palace and a tribal granary.
Most hillfort had gone out of use by the time the Romans arrived, although a few were re-occupied and defended. But the forts were no match for trained soldiers.
