Plas Berw is located to the south of Llangefni, on an ancient site recorded in the medieval period. The present seventeenth-century mansion (nprn 15801) followed a fifteenth-century predecessor the ruins of which are nearby (15801). Both lie within a former deer park (700311).
The garden area at Plas Berw at present is very small, and although the utilitarian area was once a good size, the ornamental garden was probably never extensive. The remains comprise the courtyard garden, another partly walled garden to the south-west of the house, and the area of the derelict fifteenth-century house now used as garden space (265407). 

The most important remaining part of the garden is the small, seventeenth-century walled courtyard garden in front of the main house, contemporary with the house built in 1615. It is well preserved and has been recently excavated, confirming the date, and suggesting that it was created over a paved courtyard on the north side of the fifteenth-century hall-house, now ruined, with garden soil imported for the purpose. The current planting is modern but most of the structure is original.
The house forms the north-west side of the garden, with a step up to the door; the south-west side is the wall of the ruined hall-house, which also had a door opening on to the garden; the north-east wall is a purpose-built garden wall, with a gateway through it to the house. The south-east wall has been demolished, probably when the railway embankment was built.

Excavations were necessitated by attempts to drain the area effectively, and revealed previous attempts to solve drainage problems, due to its position at the foot of a steep slope. The surface had therefore been much disturbed. The imported soil was concentrated along the wall of the hall-house, suggesting a layout similar to today's, with borders round the edges and an open space in the middle. Its surface, apparently not paving, may have been gravel, grass, or another type of hard surface, although no direct evidence was found.

Sources:
Cadw 1998: Register of Parks and Gardens of Special Historic Interest in Wales: Conwy, Gwynedd & the Isle of Anglesey, 24-7 (ref: PGW(Gd)42(ANG).
Ordnance Survey second edition 25-inch map, sheet: Anglesey XVIII.11 (1900).

RCAHMW, 27 June 2022