1. Cadw SAM No.=BR052
2. An elongated hillfort, 150m by 35m, resting on natural scarps to the S, and defined by a degraded bank and ditch, with scarps possibly representing a further line of banks and ditches.
(source OS495 card; SO03NW1)
3. 1986 Brecknock Inventory description. (HF 37) Gaer Fawr. A srnall, bivallate fort encloses the summit of the terminal spur of the Allt Arnog ridge, 3.5 km E. of Merthyr Cynog. The elongated-oval plan of the site is formed by precipitous natural defences on the S and curving, bivallate fortifications on the other sides, enclosing an area sloping downwards from S. to N. from a maximum altitude of 388 m above O.D. The ground beyond the defences falls away steeply on the N. and S.W. and the least arduous approach to the site is from the N.E. where a low saddle separates it from the main ridge.
Lying in improved grassland, the fortifications are well preserved despite some damage by ploughing especially to the outer ditch. A modern field bank and ditch impinge on the W. end of the earthworks and a modern fence occupies the crest of the outer rampart. The enclosure measures internally 155 m E. to W. by 40 m, an area of 0.48 ha. The inner rampart is curved back on the W. to join the natural slope but on the E. stops short of the precipice to allow access to the interior. The inner face of the bank is preserved best on the W. where it is 0.9 m high. The outer scarp is up to 3 m high. The earth and rubble comprising the bank were obtained probably from the fronting ditch and an internal quarry ditch of which there are slight indications along the N. side. Most of the inner ditch has been reduced to a shelf at the toe of the rampart but a shallow depression at the W. end, and a hollow and slight counterscarp bank 0.6 m high on the E. are still visible. Between 5 m and 10 m in front of the inner ditch is the outer rampart which has been reduced to a stony, outward-facing scarp up to 2.75 m high. Ploughing has obscured the full extent of the Wend of the bank which does not seem to have been continued round to correspond to the inner rampart since there is no trace of it on the uncultivated ground above the natural S. slope. A shelf running the length of the rampart toe probably represents the site of the outer ditch. There is no trace of the counterscarp bank noted by R. E. Kay.
The entrance is on the E. through simple gaps between the ends of the ramparts and the natural slope. The inner rampart appears to have been strengthened "ere but there is no trace of the inturn indicated by Kay.Traffic crossing towards a wet hollow about 50 m outside the enclosure has eroded both ramparts l n corresponding positions towards the W. end of the N. side for a length of about 10 m. The use of this route rather than a more direct one suggest there may nave been narrow gaps in the original works. There are no ancient features visible in the interior except the quarry ditch.
Reference:
RCAHMW 1986. An Inventory of the Ancient Monuments in Brecknock (Brycheiniog). The Prehistoric and Roman Monuments. Part ii: Hill-forts ad Roman Remains. HMSO. pp75-77