Tre'r Ceiri is one of the most spectacular ancient monuments in Wales. The settlement is surrounded by stone walls that are largely intact, and which reach up to 4 meters on some places. Within the walls are ruins of about 150 stone houses, which would have had turf roofs. During Roman times, it may have housed up to 400 people. Historian John Davies suggests that because the settlement is so far above sea level, the huts served as habitations for summer shepherds who also had winter dwellings in the lowlands.