Caer Siac is the name given to the mutilated remains of a small motte that is located on a natural ridge. The diameter of the motte is 24m across and it is 2m high. The slight earthworks to the north-east are thought to be a bailey. There are subsidary enclosures to the north-east and south-west, and ditches that are 5m wide and 0.6m deep. The name 'Caer Siac' is thought to have evolved from the name of a nearby field known as 'Cae Siac'. The site was visited by the RCAHMW on 28 October 1909 and by Clwyd-Powys Archaeological Trust in 1972 and 1978.

Claire Parry, RCAHMW, 11 August 2011.

Sources:
Inventory of the Ancient Monuments in Wales and Monmouth I - County of Montgomery , Royal Commission on the Ancient and Historical Monuments of Wales , 1911
Clwyd-Powys Archaeological Trust Historic Environment Record