Cefn Mably House, a mostly eighteenth-century house now converted to private appartments (nprn 18286), is located on the north-west side of the Rhymney valley, to the north of Cardiff. It lies within a medium-sized landscape park set on rolling ground. It dates from the late sixteenth century, through 1709-35; to the nineteenth century. The house itself is surrounded by gardens (see 265747 & 700160).

The park has probably evolved over a long period but its early history is obscure. Its present form developed from the early eighteenth century and reached its maximum extent in the late nineteenth century when the general configuration of open ground and woodland was by then established. Compared to now there were then more clumps and individual trees. The park is much reduced, large areas having been developed and woodland to the north converted to forestry plantations. What remains forms an irregular oval.

The main entrance lies on the east boundary just west of the Cefn-llwyd bridge over the river Rhymney, Cefn Mably Lodge to its north. The drive, intermittently flanked by trees, approaches the north side of the house . A secondary drive from the Maes-y-bryn on the south boundary was also once flanked by trees. 

South of the house the ground drops steeply from the garden towards the valley flood plain. Small areas of woodland lie to the south-west, and further south the ground rises to a narrow ridge. Plantings are mostly deciduous, the most prominent being a row of oak clumps along the top of the ridge visible from the house and from a wide area beyond the park to the south. The steep slopes and mature trees together form a beautiful setting for the house.

Near the western edge of the field below the house is a copse of large ancient sweet chestnuts, their residual arrangement in rows suggesting relics of an early formal park layout. In the field to the west, beyond the garden, there are some large beeches at its north end and a single mature evergreen oak at its north-west end. 

To the north of the west drive is an area of cultivated ground, retaining a few clumps of trees. Further north is a large forestry plantation, Coed Cae-ffynnon which, in the nineteenth century, was seemingly partitioned.by a gridiron layout of paths.

Sources:
Cadw 2000: Register of Parks and Gardens of Special Historic Interest in Wales, Glamorgan, 24-8 (ref: PGW(Gm)11(CAE)).
Ordnance Survey Second Edition 25-inch map, sheet: Glamorgan XXXVII.12 (1875).

RCAHMW, 13 May 2022