Earthworks remains of Trwyn Du building are depicted on the 1st edition OS County series (Anglesey XXI.7 1889), but not on later editions. The building was about 14m by 6.3m and was subdivided internally. It may have been a house or farmbuilding.
The earthworks take the form of an apparent penanular bank, about 6.0m across and 0.5m high, with an attached linear bank. It was previously identified as a later Prehistoric type roundhouse settlement.

John Wiles 15.08.07