At the eastern edge of Portskewett, in a privately owned field opposite Black Rock Road, very near to the Leechpool turn, is evidence of a significant neolithic chambered tomb or long barrow.

A small group of puddingstones mark the entrance of the site known as Heston Brake. Human skeletons, cattle bones and some pottery were discovered in the chamber when it was excavated in 1888.

The stones can be reached by following the public footpath accessed via the kissing gate which is situated on the left  about 150 metres from the main road toward Leechpool.

In his 1954 Monmouthshire Sketch Book Hando writes: "Garn Llwyd, Gwern-y-Cleppa and Heston Brake are our three outstanding dolmens".