The Senghenydd Dyke is a bank and ditch that runs for roughly 12km enclosing the Aber valley in the Glamorgan uplands, including the modern villages of Senghenydd and Abertridwr. It consists of a bank with an internal ditch and is thought to have supported the pale or deer fence of a vast medieval deer park roughly 4.0km north-south by 3.0km, some 1,000ha (roughly 2,500 acres) in extent. The dyke faces inwards to prevent the deer escaping. There are additional stretches of dyke attached to the north-west side of the main circuit (NPRN 301281; 307765), these appear to be contemporary with or later than the park circuit.

The dyke survives as an earthwork feature through most of its course, which is sometimes followed by current field boundaries. It consists of a bank from 3.1m to 6.7m wide and up to 0.6-1.2m high, with a flat-bottomed ditch from 2.7m to 5.5m wide and 1.2-1.5m deep. There are no obvious surviving entrances, only breaks across marshy areas.

The creation of such a vast deer part, presumably involving the depopulation of the entire valley, is most likely to have occurred in the aftermath of the annexation of Senghenydd Is Caeach by the lord of Glamorgan in 1267 and can be linked to the construction of the vast castle of Caerphilly 3.0km to the south-east (NPRN 94497). It seems likely that the route from the castle's western entrance followed the Nant-yr-Aber and the main entrance to the park was by the stream at the base of what was here a steep wooded valley. The park would have been the setting for highly formalised aristocratic hunts. There was probably at least one lodge housing the parker and providing passing accommodation for the lordly hunters. A possible location is at Abertridwr, where there was a wood named Coed Tyn'-y-parc (at ST1181 8952).

The Aber valley was heavily industrialised in the late nineteenth-early twentieth century. Its former condition can be seen on the 1st edition OS County series of 1875-81 (Glamorgan XXVIII.7-8, 12-13, 16).

Comprises:
Northern section (NPRN 400446).

Source: RCAHMW Glamorgan Inventory III.2 Medieval Secular Monuments: Non-defensive (1982), 381-2 MI 75

John Wiles 04.02.08