The landscape area of Gelligaer Common represents an increasingly rare survival in South East Wales of an area of high upland moor rich in a diverse archaeological resource. The Common and the area lying immediately to the south east is about 8 kms long and l km wide and extends from the pivotal ancient settlement of Gelligaer in the south east to the summits of Pen Garnbugail and Mynydd Fochriw in the north west. The ridgetop occupied by the Common rises gently from about 250m above OD at Gelligaer to over 470m above OD at the rounded summits of Pen Garnbugail and Mynydd Fochriw. However, on either side of the Common, and outside the area described here, slopes tumble steeply into Cwm Bargoed on the west and into the valley of the Bargoed Rhymney on the east, tributaries to the major valleys of the Taf and Rhymney respectively.
The area varies considerably from the moorland plateau of the Common in the north west, with isolated farms and improved, enclosed pasture on its western and eastern flanks, to the enclosed farmland of the south east and the pleasant rural village of Gelligaer which is now adjacent to a primarily industrial urban landscape of the Rhymney Valley. The landscape is diverse both in its form and in its archaeological and historical content, which displays a remarkable continuity of occupation.