The distribution of prehistoric finds in the region is clearly related to the topography.
The area lies across the boundary of the highland and lowland zones of Britain. In the north and west the high ground, rising in most parts well above the 1,000-foot contour, forms the south-eastern margin of the highland massif of central Wales. It is sharply dissected by river valleys draining south-eastwards, which provide easy routes for the penetration of settlement and trade from the coast, but restrict movement in an east—west direction. By contrast, the coastal plain forms a westward extension of the lowland zone of England, and presents few barriers to movement, either along the coast or across the Bristol Channel to the opposite shores of Gloucestershire and Somerset.

Evidence for pre-neolithic settlement in the region is scanty. The industries of the Lower Palaeolithic are represented by the solitary find of an Acheulean hand-axe of quartzite from Penylan, an eastern suburb of Cardiff; and those of the Upper Palaeolithic are restricted to King Arthur's Cave, near Ross-on-Wye. The same site has yielded, at a higher level, a microlithic assemblage assignable to the Mesolithic; but elsewhere this period is represented only by numerous microliths from the sand dunes of Merthyr Mawr Warren, south-west of Bridgend. It is probable, however, that many other sites have been lost through the extensive coastal submergence which is known to have occurred during and since Boreal times.

The first evidence of large-scale human penetration of the area is provided by the megalithic tombs which form two distinct groups, one inland, to the east and south-east of Brecon, and the other less compactly distributed in the Vale of Glamorgan. An isolated site at Heston Brake, south-west of Chepstow, contains a chamber in the form of a long narrow gallery, and may perhaps represent a direct link with the West French type of gallery grave (allee couverte). The remaining tombs in both groups are of the Severn–Cotswold type. In spite of their westerly position in relation to the main concentration of these tombs in England, it seems improbable that they represent direct colonization by sea from southern Brittany, where the prototypes of the transepted form of gallery grave have long been recognized. Neither group in the region contains an axial transepted gallery, of the type of West Kennet or Stoney Littleton, a feature generally regarded as early in the tomb sequence; while the cairns, like their Cotswold neighbours, are markedly rectangular or trapezoid in plan, and cannot be paralleled in France. It is thus probable that both groups are the result of secondary colonizations of tomb-builders from across the Bristol Channel; and this is in some degree confirmed by the fragmentary pottery from two sites (Tinkinswood, west of Cardiff, and Ty Isaf in Brecknockshire), which suggests origins in the Windmill Hill culture of Wessex rather than further to the west and south.

Other evidence of Primary Neolithic activity is restricted to stray finds of stone axes and leaf-shaped flint arrowheads, the great majority coming from the coastal plain, though there are some signs of penetration up the valleys, particularly that of the Usk. The occurrence of small hoards of axes near Cardiff and Newport points, perhaps, to the existence of 'ports' there even at this early date. No settlement sites have yet been found, and it is thus not possible, in the present state of knowledge, to distinguish in the region any Primary Neolithic culture other than that of the chambered tombs.
Secondary Neolithic settlement has so far been recognized only at two sites, Cefn Cilsanws in southern Brecknockshire and Saint-y-Nyll near Cardiff. At both, small timber structures have been found, associated at the former with a sherd of Peterborough ware and at the latter, beneath a cairn covering a cremation, with pottery resembling the Fengate type. Otherwise the Secondary Neolithic cultures are represented only by a few stray finds of stone mace-heads and petit-tranchetderivative arrowheads. This paucity of material may perhaps reflect the poor representation in the area of the Mesolithic cultures from which the Secondary Neolithic springs; though it must be remembered that many of the numerous stone axes in the district are likely to be the products of the Secondary Neolithic axe-factories located further to the west and north.
With the arrival of Beaker people, probably during the seventeenth century B.C., south-east Wales takes on a new importance. Over forty per cent of all beakers hitherto recorded from Wales have been found within the comparatively small area covered by Fig. 13. The main concentration lies in the Vale of Glamorgan and its immediate hinterland, especially on the sand dunes of Merthyr Mawr Warren. The isolated group on the southern foothills of the Brecon Beacons is presumably the result of a movement inland up the valley of the Taff.

All three of the principal varieties of beaker (Abercromby's types A, B and C) are represented, and in each case there can be little doubt that a secondary colonization from southern England is involved. In the absence of any beaker burials from Monmouthshire, such colonization is more likely to have been by sea, across the Bristol Channel; and it should be noted that the best parallels for the distinctive 'bar-chevron' ornament of many of the A beakers are to be found in Somerset.

This concentration of Beaker material must surely be related to the introduction of metal-working into Britain at this time, and the establishment along the south coast of Wales of a trade route between Ireland and the principal areas of Beaker settlement in southern England. It is against this background of economic links between Wessex and the West that we must see the transport of the Stonehenge bluestones from Pembrokeshire.

The succeeding Early Bronze Age, of the sixteenth and fifteenth centuries B.C., is characterized in southern England by the burials of the rich Wessex Culture; and in view of the known dependence of this culture upon Irish metal resources (and for gold in particular), one might expect settlement and trade along the south Welsh coast to be intensive at this time. In fact, however, evidence for the penetration of the Wessex Culture into the region is surprisingly slight. Burials are confined to a single bell-barrow, at Crick in Monmouthshire, and to the well-known Breach Farm site near Cowbridge in the Vale of Glamorgan; otherwise the culture is represented by no more than three or four stray finds of bronzes, all from the southern part of the region.

The scarcity of this material must reflect some radical shift in the route connecting Ireland with southern England in the middle of the second millennium B.C. ; and this is confirmed by the otherwise northerly distribution of objects and burials of Wessex type in Wales, a pattern apparently related to the use of the Severn valley route.

There is, however, no lack of evidence for a numerous population in the region in the latter half of the second millenium, as is shown by the dense concentration of barrows and cairns. Their distribution, whether of groups or of single monuments, shows a very marked preference for high ground, apart from a compact group in the western part of the Vale of Glamorgan, which includes the well-known turf barrows with internal stake circles excavated by Sir Cyril Fox.
The majority of these sites are still unexplored; but the excavated examples have yielded only cremated burials, and it appears that in this region the inhumation rite does not outlast the Beaker cultures, and was obsolete soon after 1500 B.C. The associated grave-goods include enlarged food-vessels, cinerary urns and pygmy cups, but there is at present insufficient evidence to allow any distinction to be made between these types in date or distribution. It may be noted, however, that barrows and cairns are rare in Monmouthshire, especially in the lowland area of the county; and that so far pottery of the Early and Middle Bronze Age is confined to a single cinerary urn. The marked paucity of finds of the second millennium B.C. in this eastern part of the region suggests that the Forest of Dean formed a natural barrier to communication with the Cotswold area by land through Gloucestershire; so that as in the Neolithic period the easiest communications with the east lay across the Bristol Channel.

There is some evidence, however, that in the latter part of the Middle Bronze Age contact between South Wales and Somerset was broken. Iimplements of Middle Bronze Age type (rapiers and broad-bladed palstaves, with and without loops) are relatively scarce, and occur chiefly in the coastal plain, with only slight penetration of the valleys to the north. There is a notable absence of any of the exotic objects of North European origin (ridge-button sickles, bronze torcs, ribbed armlets and loop-headed pins) which are the most striking features of the Somerset hoards of this period.