There are almost six hundred hill-forts in Wales, if it is accepted that the term embraces a host of small enclosures as well as forts of six hectares or more. The two hundred or so which extend over less than half a hectare were probably individual fortified farms. The middle-sized structures are considered to be folds for animals, sacred enclosures, centres for seasonal agricultural activities, occasional refuges or the strongholds of petty chieftains. There are twenty-two which exceed six hectares, and these provided protection for the homes of a substantial number of people, proof that the economy in the last centuries of prehistory, in some parts of Wales at least, was capable of sustaining quasi-urban communities.

The hill-forts are the earliest constructions in Wales to have clear military implications; their existence suggest the growth of the territorial principle and the need or the desire to defend that principle. They also suggest that the population was less nomadic in the centuries after 1000 B.C. than it is believed to have been in the Bronze Age. On the basis of the remains discovered in the few hill-forts that have been excavated, it can be assumed that mixed, settled farming was the basis of the economy. Querns (handmills) have been found in the forts of Dinorben and Mynydd Conwy, an indication that grain was grown; nevertheless, the heaps of bones discovered at Coygan and Pendinas (Aberystwyth) indicate that stock-raising was the chief activity. The hill-forts, in particular the most elaborate, are proof that their designers had skills of a high order, although too much should not be claimed for them in view of the fact that the Parthenon at Athens, which was begun in 477 B.C., is earlier than most of them. They are also proof of the existence of a hierarchical society in which a ruling class had the power to force others to undertake back-breaking toil, and few tasks can have been more exhausting than the building of forts such as Llanymynech, Caer Goch or Pendinas.

The hill-forts of Wales were constructed over a period of a thousand years. They vary in their nature and distribution from one to another, a fact which throws light upon the social and political order in the different regions of Wales. They are at their most numerous in the south-west, where there are more than a hundred and fify fortlets of under half a hectare. Many of these consist merely of a dyke and a ditch across a promontory above the sea -- cliff castles similar to those which dot the coasts of Cornwall. Walesland, one of the raths which are so common in western Dyfed, has been thoroughly excavated. Within its unmortared stone walls are the remains of six round huts which were built and rebuilt over the period of 250 B.C. to A.D. 250. From later evidence, it is known that south-west Wales was the territory of the Demetae. The multiplicity of small forts and the scarcity of larger fortifications among them suggests that the Demetae were organized in family groups and that they lacked any substantial central authority.

from A History of Wales by John Davies