The place-names of Wales derive in most cases from the Welsh language, but have been influenced by linguistic contact with the Romans, Anglo-Saxons, Anglo-Normans and modern English. The study of place-names in Wales reveals significant features of the country's history and geography, as well as the development of the Welsh language. See: History of WalesDuring the 4th to 11th centuries, while Anglo-Saxons and other migrants from Europe settled adjoining areas of Britain, Wales developed as a distinctive entity, developing its language, legal code, political structures. By stages between the 11th and 16th centuries, Wales was subdued and incorporated into the Kingdom of England while still retaining many distinct cultural features, most notably its language. Since there has been a mixing of cultures in Wales, with the English language dominant in industry and commerce, but with Welsh remaining as a living language in its stronghold, y Fro Gymraeg or "Welsh language country" in northwest, mid- and west Wales.
Welsh culture and political autonomy has been reasserted since the mid 19th century. See: Welsh language and History of the Welsh languageThe Welsh language is a Western Brittonic language descended from the Common Brittonic spoken throughout Britain in the centuries before the Anglo-Saxon and Viking invasions that led to the creation of England. Many place-names in Britain of natural features such as rivers and hills, derive directly from Common Brittonic. Obvious examples of place-names of Welsh origin include Penrith and the numerous Rivers Avon, from the Welsh afon. Place-names from the Western Brittonic-speaking Hen Ogledd occur in Cumbria and the Scottish Lowlands; these include the name of Edinburgh, from Cumbric Din Eidin "Eidin's Fort". The Cornish language is a Southwestern Brittonic language and many place-names in Cornwall and to a lesser extent neighbouring Devon and Dorset therefore have similar origins to names in Wales, such as the River Avon, Devon; the settlement name Tre- is identical to that used in Welsh and is among the most common placename elements in both Wales and Cornwall equating to English -ton, alongside Lan- equating to Welsh Llan- combined with the name of a Saint.
In Devon the prevalent use of -combe reflects an early English borrowing of Cornish/Welsh cwm. Welsh remains a living language, spoken by over 20% of the country's population. Like all languages, it has changed over time and continues to do so, for instance by accepting loan words from other languages such as Latin and English; the Welsh language itself has many characteristics unfamiliar to most English speakers that can make it difficult to understand its place-names. For example, it uses a number of initial consonant changes in different grammatical circumstances. In relation to place-names, this means that, for example, a parish dedicated to one of the saints Mary becomes Llanfair – the initial m of Mair changes to f for grammatical reasons. Other changes can apply to internal vowels. There are differences between Welsh and English spelling standards, which have affected how place-names are spelled in the two languages. For instance, a single f in Welsh is always pronounced /v/, while ff is pronounced /f/.
The study of Welsh place-names is promoted by the Welsh Place-Name Society. Early inhabitants of Wales gave names first to noteworthy natural features, such as rivers, mountains and shores. However, before the Roman occupation in the first century, there seems to have been little tradition in Wales of people coming together in organised settlements, so little reason to give names to such places; the Roman towns which were established were fortified and were given the generic name of castra, which in Welsh became caer with the meaning of "fortified enclosure". Many of these continued as towns after the Romans left, including Caernarfon, Carmarthen and Caerwent. Elsewhere, many villages and towns took their names from natural features. For example, Abergele refers to the "mouth of the Gele", Harlech means "fair rock", Rhuddlan "red bank", Porthcawl "harbour with sea-kale". Aberystwyth means "mouth of the Ystwyth", a river a mile or so away from the town centre, was so named as a result of confusion by the English over the different castles in the area.
Many others took their name from religious settlements and clasau established from the fifth century onwards. These use the prefix llan equivalent to "parish". Most of them are dedicated to their founders, who hailed from local dynasties and were venerated as patron saints. Examples include Llandudno and Llantwit. Following the Norman invasion of Wales, some were rededicated to more generic saints: Llanilar, Llanfoist. A few—usually by mistake—include other elements or none at all: Llan, Llanharry, Llangefni. Other religious place-names eglwys. Over the centuries, Welsh place-names have been variously affected by social and economic changes in the country; the Industrial Revolution saw the development of many new towns and villages in south Wales. Some of these used existing place-names, while others acquired new names. For example, the towns of Port Talbot and Tredegar took the names of their main la