This circular earthwork mound measures about 35m in diameter. It is surrounded by a ditch which is now more obvious as a cropmark than it was at the time of the Ordnance Survey in the late 1860s, but was shown by excavation to be up to 12m wide. The SE side is obscured by a field boundary, which curves slightly in respect. The site was traditionally known as the Round Table, but excavation by Gerhard Bersu in 1942-43, and subsequent reporting published in 1977, established the site's name as Ballanorris.


Bersu's investigations revealed a single circular building with a substantial 6-8m wide earth and stone outer bank for a wall and a roof supported on roughly circular concentric rings of timber posts, which also served to define spaces within the structure. There was a central hearth and a doorway facing SSW covered by a timber framed porch or entrance-way leading through the substantial outer bank or wall. The building was roofed with turf.


Reinvestigation by Harold Mytum (Centre for Manx Studies, University of Liverpool) in 2011 suggests that the outer bank was a separate defensible structure, crowned by a palisade near the top of its inward slope, and that the concentric posts supported a raised timber floor on which was built a single timber roundhouse of a diameter of perhaps 12m. Mytum also suggests that the entrance 'porch' may in fact represent a defensible timber gateway structure with a wooden tower above. Soil analysis further suggests that the site might initially have been used to pen livestock before being converted for domestic use.