 Although little evidence of settlements has been found in the Rhondda that date between the Neolithic and Bronze Age periods , several cairns and cists have been discovered throughout the length of both valleys . The best example of a round @-@ cairn was found at Crug yr Afan , near the summit of Graig Fawr , west of Cwmparc . The cairn consisted of an earthen mound with a surrounding ditch 28 metres in circumference and over 2 metres tall . Although most cairns discovered in the area are round , a ring cairn or cairn circle exists on Gelli Mountain . Known as the ' Rhondda Stonehenge ' the cairn consists of 10 upright stones no more than 60 cm in height encircling a central cist . All the cairns found within the Rhondda are located on high ground , many on ridgeways , and may have been used as waypoints . 
