Wales is the upland western peninsula of Great Britain, bordered by England to the east, the Irish Sea to the north and west and the Bristol Channel to the south. It covers about 20,641 km², runs roughly 274 km from north to south, and has a mainland-plus-Anglesey coastline of about 2,704 km. Its physical regions are the mountains of Eryri (Snowdonia) in the north-west, the island of Anglesey and the Llŷn Peninsula, the Clwydian hills of the north-east, the rounded Cambrian Mountains of mid Wales, the sandstone escarpments of Bannau Brycheiniog (the Brecon Beacons), the coalfield valleys of the south, and the coastal lowlands of Pembrokeshire, Gower and the Vale of Glamorgan. The highest point is Yr Wyddfa (Snowdon) at 1,085 m. The main rivers are the Severn (354 km, the longest in Great Britain), the Wye (about 250 km), the Dee and the Tywi, at about 120 km one of the longest rivers that flow entirely within Wales.
Eryri: Snowdon’s Ordovician Volcanoes and the Welsh 3000s
The north-west corner of Wales holds every one of the country’s mountains above 3,000 feet (914 m). There are 15 of them, known as the Welsh 3000s, and they sit in three tight ranges: the Snowdon massif, the Glyderau and the Carneddau. They are close enough together to be climbed in one day; Finlay Wild set the record of 4 hours 10 minutes from first peak to last in 2019.
The rock is volcanic. During the Ordovician period, between about 485 and 460 million years ago, a large volcanic system centred on what is now Snowdon emitted an estimated 60 km³ of debris. Ice then carved that rock during the Pleistocene, and the mountains took their present shape in the last glaciation, the Devensian. The result: the pyramidal summit of Yr Wyddfa, the knife-edge arêtes of Crib Goch and Y Lliwedd, and corrie lakes such as Llyn Llydaw, which covers 45 hectares on the mountain’s eastern flank at 440 m.
Snowdonia National Park, designated in October 1951 as the first of Wales’s three national parks, now covers 2,130 km² and extends south over the Rhinogydd, the Aran range and Cadair Idris, the long ridge above Dolgellau whose cwms, moraines and roches moutonnées are a glacial textbook of their own. Snowdon is often called the UK’s busiest mountain: 543,541 walkers climbed it in 2022, and the rack railway from Llanberis, open since 1896, runs 7.6 km to the summit station. The western mountains also take the heaviest rain in Wales, with annual totals above 3,000 mm on the high ground.
Anglesey, the Menai Strait and Llŷn
Below the mountains the land drops to the lowest, gentlest country in the north. The island of Anglesey (Ynys Môn) covers 676 km², which makes it the largest island in Wales and in the Irish Sea. Some of the oldest rocks in Wales, Precambrian outcrops around 700 million years old, are exposed here and on the Llŷn Peninsula. Parys Mountain, at its height, was the largest copper mine in the world.
The island is cut off by the Menai Strait, a channel about 25 km long that varies in width from 400 m between Fort Belan and Abermenai Point to 7.5 km at its north-eastern end. Ice sheets scoured it out along the Menai Strait fault system. Differential tides at its two ends drive fierce currents through the Swellies, the rocky stretch between Thomas Telford’s Menai Suspension Bridge of 1826 and Robert Stephenson’s Britannia Bridge of 1850.
To the south-west, the Llŷn Peninsula projects about 50 km into the Irish Sea, enclosing Tremadog Bay, the northern arm of Cardigan Bay. Cardigan Bay itself, between Bardsey Island and Strumble Head, is the largest bay in Wales.
The Clwydian Range and the Dee Valley
The north-east is border country. The Clwydian Range runs north from Llandegla to Prestatyn and peaks at Moel Famau, 554 m. Its steep west-facing scarp is a fault line: the Vale of Clwyd Fault drops the younger Carboniferous and Permo-Triassic rocks of the vale below the Silurian mudstones and sandstones of the hills.
South of the hills runs the River Dee. It rises on Dduallt in southern Snowdonia and passes through Llyn Tegid (Bala Lake), the largest natural lake in Wales at 4.7 km², which sits in a glacial valley dammed by a terminal moraine. Downstream, part of the Dee forms the boundary with England before reaching its estuary on Liverpool Bay. The border itself roughly follows Offa’s Dyke, the earthwork traditionally dated to the late eighth century; the 285 km Offa’s Dyke Path, opened on 10 July 1971, keeps company with its remains for about 97 km.
Pumlumon and the Cambrian Mountains: Source of the Severn and Wye
The Cambrian Mountains fill the middle of the country, running north-east to south-west. Compared with Eryri they are rounded and undulating, covered in moorland, blanket bog and tussocky grass. Their highest point is Pen Pumlumon Fawr on the Plynlimon massif, at 752 m. The Welsh name Pumlumon is thought to mean “five tops” or “five beacons”.
Plynlimon is the great watershed of Wales. The Severn rises on it at about 610 m, near the Ceredigion–Powys border, and flows east into Shropshire, Worcestershire and Gloucestershire to become the longest river in Great Britain. The Wye rises on the same massif and travels about 250 km to the Severn Estuary, its lower reaches forming part of the England–Wales border. Further south, the Tywi rises in the same uplands and runs about 120 km south-west through Llandovery, Llandeilo and Carmarthen.
Much of the water never reaches those rivers. The five Elan Valley reservoirs, Claerwen, Craig-goch, Pen-y-garreg, Garreg-ddu and Caban-coch, were built for Birmingham Corporation between 1893 and 1952 under an Act of 1892. Their water flows by gravity along a 117 km aqueduct, opened in 1906, to Frankley Reservoir. Llyn Brianne, dammed on the upper Tywi in 1972, stores winter rain for supplies to south-east Wales.
The rock here is mostly the Lower Palaeozoic sediment of the Welsh Basin. Turbidites, layers laid down by submarine avalanches and sorted by grain size as they settled, show clearly in the sea cliffs around Aberystwyth. Wales gave geology some of its vocabulary: the Cambrian period takes its name from Cambria, the Latin name for Wales, while the Ordovician and Silurian are named after two pre-Roman tribes of Wales, the Ordovices and the Silures.
Bannau Brycheiniog: The Old Red Sandstone Escarpments
South of the Cambrian Mountains, the uplands change character. Bannau Brycheiniog, the Brecon Beacons, is carved from Old Red Sandstone, the debris eroded from the Caledonian mountains that rose as the sea retreated from the Welsh Basin around 420 million years ago. The strata dip gently to the south, so the ranges present long grassy slopes on that side and steep north-facing escarpments on the other.
The central summit is Pen y Fan, at 886 m the highest British peak south of Cadair Idris, with its twin Corn Du at 871 m. The fan in its name is a mutated ban, “peak”; the plural, bannau, gives the range its Welsh name. The national park, founded in 1957 as the last of the three in Wales, covers 1,344 km² and spans three separate ranges: the Black Mountains in the east, rising to Waun Fach at 811 m and running over the border into England; the central Beacons and Fforest Fawr; and, confusingly, the single Black Mountain (Y Mynydd Du) in the west, topped by Fan Brycheiniog at 802.5 m.
The South Wales Valleys and the Coalfield Plateau
Immediately south of the Beacons lies what was Britain’s only mountainous coalfield. The South Wales Coalfield is a synclinorium, a great down-fold of Carboniferous rock that stretches from Pembrokeshire to Torfaen. Its surface is a plateau of moorland at 300 to 600 m, cut by steep, parallel valleys running roughly north to south: the Rhondda Fawr and Rhondda Fach, the Cynon, the Taff, the Rhymney and the Ebbw among them.
The coal measures formed in swamps during the late Carboniferous, and the coal increases in rank from east to west, from bituminous coal in the east to anthracite north and west of Neath. Above the coal lies Pennant Sandstone, which forms the plateau surface and was much used in local building. The Rhondda’s steam coal fuelled the steamships of the 19th and early 20th centuries, and deep mining boomed there from about 1850 to the First World War. Routes along the valley floors carried it south to the docks at Newport, Cardiff and Barry, and the ports of Swansea, Cardiff and Newport grew on the export trade. The last deep pit in Wales closed in 2008, but the pattern the coalfield set, ribbon towns along valley floors with open moorland on the ridges between, still shapes the region.
Pembrokeshire, Gower and the Vale of Glamorgan
The southern coastal lowlands are where Wales flattens out. In the far south-west, the Pembrokeshire Coast National Park, established in 1952, covers about 420 km of coastline and is the only national park in the United Kingdom made up largely of coastal landscape. Its centrepiece is Milford Haven, a ria, or drowned river valley, flooded at the end of the last ice age and one of the deepest natural harbours in the world. Inland, the Preseli Hills rise to Foel Cwmcerwyn at 536 m. Their dolerite outcrops have been proposed as a source of the Stonehenge bluestones since the petrologist Herbert Henry Thomas made the case in 1923, though which outcrops supplied the stones is still argued over.
Further east, the Gower Peninsula covers about 180 km² of limestone cliffs, caves and beaches between the Loughor Estuary and Swansea Bay. In 1956 it became the first Area of Outstanding Natural Beauty in the United Kingdom; at its western tip, Rhossili’s sandy beach runs for 4.5 km. West of Cardiff, the Vale of Glamorgan holds some of the best farmland in a country where only about 6% of the land is arable. It faces the Severn Estuary, whose tidal range reaches about 15 m, and Rhoose, home of Cardiff Airport, recorded the strongest lowland gust in Wales, 200 km/h, on 28 October 1989.
Climate follows the same regional pattern as the rock. The mean annual temperature is about 11 °C on the coast, and it falls by roughly 0.5 °C for every 100 m of height, to about 5 °C on the tops of Eryri. The lowest temperature on record, −23.3 °C, was measured at Rhayader in the Cambrian uplands on New Year’s Day 1940. For a closer look at the highest of these regions, see the Snowdonia National Park guide; to compare Wales with the much larger Highland country to the north, read about Scotland’s geography, or untangle how Wales fits into Britain in UK vs Great Britain vs England.