The Royal Observer Corps Monitoring Post comprises an 'Orlit A' surface observation post and adjacent underground monitoring post. Both date to the Cold War era and are located on a local summit. The 'Orlit A' post was used between 1952-60 and the underground monitoring post was built in 1960 and decommissioned in 1991. The 'Orlit A' post was constructed of bolt-together prefabricated concrete panels and measured 1.6 metres in height, 3.05 metres in length and 2.03 metres in width.

The underground monitoring post, situated north of the 'Orlit A' post, is protected by a grassed mound of earth and rock which measures 1 metre in height, 15 metres in length and 14 metres in width. The combined entrance, ventilator stack and Ground Zero Indicator mount are located at the south end and a second ventilator stack is located at the north end. A connector box, together with three concrete anchor posts for the VHF aerial mast demonstrate that this was a Master post for a cluster of three, the others being in Llanidloes and Rhayader.
Source: Cadw scheduling description. F.Foster/RCAHMW 22.01.2009