The Afon Cynrig is a river in Powys

Powys

Powys is a local-government county and preserved county in Wales.-Geography:Powys covers the historic counties of Montgomeryshire and Radnorshire, most of Brecknockshire , and a small part of Denbighshire — an area of 5,179 km², making it the largest county in Wales by land area.It is...

, Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 whose headwaters rise in the central Brecon Beacons

Brecon Beacons

The Brecon Beacons is a mountain range in South Wales. In a narrow sense, the name refers to the range of popular peaks south of Brecon, including South Wales' highest mountain, Pen y Fan, and which together form the central section of the Brecon Beacons National Park...

 and flow northwards to join the River Usk

River Usk

The River Usk rises on the northern slopes of the Black Mountain of mid-Wales, in the easternmost part of the Brecon Beacons National Park. Initially it flows north into Usk Reservoir, then east by Sennybridge to Brecon before turning southeast to flow by Talybont-on-Usk, Crickhowell and...

 at Abercynrig just east of Brecon

Brecon

Brecon is a long-established market town and community in southern Powys, Mid Wales, with a population of 7,901. It was the county town of the historic county of Brecknockshire; although its role as such was eclipsed with the formation of Powys, it remains an important local centre...

.

Two rivers combine to form the Cynrig just above Cantref - these being the Nant Sere and the Nant Cynwyn. They rise in two magnificent glacially carved valley heads beneath the peaks of Pen y Fan

Pen y Fan

Pen y Fan is the highest peak in South Wales and southern Britain, situated in the Brecon Beacons National Park. At above sea-level, it is also the highest peak in Britain south of the Snowdonia mountain range...

 and Cribyn

Cribyn (hill)

Cribyn is a mountain in the Brecon Beacons with an elevation of 795 metres.The summit lies on a ridge stretching from Talybont Reservoir in the east, to the A470 road. The ridge line to the west connects Cribyn with the peak of Pen y Fan...

 and Cribyn and Fan y Big

Fan y Big

Fan y Big is a subsidiary summit of Waun Rydd in the Brecon Beacons National Park, in southern Powys, Wales. At 719m, Fan y Big lies at the western tip of the Gwaun Cerrig Llwydion plateau...

 respectively.

The 'Gap Road', an old route from Brecon to Merthyr Tydfil

Merthyr Tydfil

Merthyr Tydfil is a town in Wales, with a population of about 30,000. Although once the largest town in Wales, it is now ranked as the 15th largest urban area in Wales. It also gives its name to a county borough, which has a population of around 55,000. It is located in the historic county of...

 takes advantage of Cwm Cynwyn and the col

Mountain pass

A mountain pass is a route through a mountain range or over a ridge. If following the lowest possible route, a pass is locally the highest point on that route...

 at its head to cross this range of mountains at the heart of the Brecon Beacons National Park. It has been suggested that it is of Roman

Roman Britain

Roman Britain was the part of the island of Great Britain controlled by the Roman Empire from AD 43 until ca. AD 410.The Romans referred to the imperial province as Britannia, which eventually comprised all of the island of Great Britain south of the fluid frontier with Caledonia...

origin.