The Afon Ysgir
The Afon Ysgir is a river which rises on the southern slopes of Mynydd Epynt in Powys, Wales. The tributaries known as Ysgir Fawr and Ysgir Fechan flow past the hamlets of Pont Rhyd-y-berry and Merthyr Cynog to combine at Pont-faen and continue past the village of Battle to join the River Usk at Aberyscir.
Near its mouth is a motte, the historic church at Aberyscir and east of the river, the Roman fort of CICVCIVM or Brecon Gaer. Along with othe tributaries of the Usk, the river is designated as a special area of conservation or 'SAC' for various species of fish including lamprey, the twaite shad and the European bullhead. 
- Ordnance Survey Explorer map OL12 'Brecon Beacons National Park: western area'
- http://www.ccw.gov.uk Countryside Council for Wales website