A sinuous leat (SO09980637-SO10000634) approximately 1.1km long (east-west), 1.5m wide and 0.7m deep at the NGR given, with a retaining bank on the south side. It began on the hillside south of Rhaslas Pond, running initially south-east and under the former Brecon & Merthyr Railway, but this section was destroyed by twentieth century land reclamation. From the railway it runs across the common towards a former reservoir (NPRN 535755), which supplied water to the Rhymney Ironworks. The leat is shown on the Ordnance Survey First Edition map of 1884.
Recorded as part of RCAHMW Uplands Initiative Project, W B Horton, H & H, 19/09/2013.