The River Ceiriog is a river in north east 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...

. It is a tributary of the River Dee. It rises on the south east slopes of Moel Fferna

Moel Fferna

Moel Fferna is a mountain in North Wales and forms part of the Berwyn range. It is the most northern outpost of the range. The summit is covered in deep heather and has a shelter carin....

 in the Berwyn Mountains, and flows through the Ceiriog Valley

Ceiriog Valley

The Ceiriog Valley or Dyffryn Ceiriog is the valley of the River Ceiriog in north-east Wales. It is also the name of a ward of the County Borough of Wrexham Until 1974 the valley was part of the traditional county of Denbighshire; then it became part of the short-lived county of Clwyd, which was...

 in Wrexham County Borough. It flows below Chirk Castle

Chirk Castle

Chirk Castle is a castle located at Chirk, Wrexham, Wales.The castle was built in 1295 by Roger Mortimer de Chirk, uncle of Roger Mortimer, 1st Earl of March as part of King Edward I's chain of fortresses across the north of Wales. It guards the entrance to the Ceiriog Valley...

 and the town of Chirk

Chirk

Chirk is a small town and local government community, the lowest tier of local government, part of Wrexham County Borough in Wales. It has a population of over 4,000....

, where the Chirk Aqueduct

Chirk Aqueduct

Chirk Aqueduct is a high and long navigable aqueduct that carries what is now the Llangollen Canal across the Ceiriog Valley near Chirk, on the England-Wales border....

 carries the Llangollen Canal

Llangollen Canal

The Llangollen Canal is a navigable canal crossing the border between England and Wales. The waterway links Llangollen in Denbighshire, north Wales, with Hurleston in south Cheshire, via the town of Ellesmere, Shropshire....

 over the river. The Ceiriog joins the Dee east of the town. In its lower reaches the river forms the border between Wales and Shropshire

Shropshire

Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...

in England.