Caer is a placename element in Welsh meaning "stronghold", "fortress", or "citadel", roughly equivalent to an Old English suffix (-ceaster) now variously written as -caster, -cester, and -chester.
The north gate of Cardiff Castle, following the old Roman fortifications and rebuilt along Roman lines.
Caernarfon derives its name from the Edwardian Caernarfon Castle
The Roman fort now known as Segontium derived its name from a latinization of the British community along the Afon Seiont
Carriden House, a refurbished Roman fort which formerly formed part of the Antonine Wall in Scotland.
The place-names of Wales derive in most cases from the Welsh language, but have also been influenced by linguistic contact with the Romans, Anglo-Saxons, Vikings, Anglo-Normans and modern English. Toponymy in Wales reveals significant features of the country's history and geography, as well as the development of the Welsh language. Its study is promoted by the Welsh Place-Name Society.
The castle at Caernarfon (meaning in Welsh "the fortress in Arfon"), which was formerly anglicised as "Carnarvon" or "Caernarvon". The name "Arfon" refers to the area "opposite Môn" or Anglesey.
St. Mary's Church (Llanfair) gave its name to the village of Llanfairpwllgwyngyll in Anglesey
