NEW TYPES OF MONUMENT
Towards the end of the Neolithic period, new types of monument start to appear. In some parts of Britain, individual burials started to replace communal burials, though none have been recognised in our area. Completely new types of monument were also introduced. These were Standing Stones and Stone Circles. Although standing stones are quite common, particularly in some areas, such as Gower, stone circles are very uncommon; only three certain examples of circles are known from the whole area, and none of these have been excavated. The sites of a few of the standing stones have been excavated archaeologically, and what little evidence we have (not all of them had been left undisturbed since they were first put up) suggests that they were put up in the period which followed the Neolithic, the Bronze Age, when metalworking was introduced and some prestige tools and weapons were made from bronze, though stone continued to be used for other tools.
As stones have also been put up in other periods too, as markers or for cattle to rub against, it is sometimes difficult to tell which stones are prehistoric and which are later. It is usually accepted that very large standing stones are probably prehistoric, but is more difficult to decide in the case of smaller stones, unless they form a part of a wider group of prehistoric monuments. Most are true standing stones, much taller than they are wide, but there are a few probable examples of recumbent stones which were set so that they were longer than they were tall; a few stones which were originally standing have now fallen over. The survey found that whereas most of the standing stones in Glamorgan were sited in lowland areas, particularly the coastal plain, in Gwent the majority were in upland areas. Most standing stones occurred singly, though two examples of rows of three stones are known, at Trellech (Monmouthshire), and at Burry on Gower (now partly destroyed), and on Grey Hill, Monmouthshire, there is a row of stones (one standing, two recumbent) close to the stone circle and probably connected with it.
All three stone circles in the area are of the same type, each with a ring of relatively small slabs of stone set on edge;. rings of standing stones do not occur. One of these circles is on Grey Hill in Monmouthshire, one on Mynydd Carnllechart north of Pontardawe, Swansea, and the third (Carn Caca) in the hills overlooking the River Neath.