Carmarthen (kɑːrˈmɑːrðən, RP: kəˈmɑːðən; Caerfyrddin kairˈvərðɪn, "Merlin's fort" or "Sea-town fort") is the county town of Carmarthenshire and a community in Wales, lying on the River Towy north of its estuary in Carmarthen Bay. The population was 14,185 in 2011, down from 15,854 in 2001, but gauged at 16,285 in 2019. It has a claim to be the oldest town in Wales – Old Carmarthen and New Carmarthen became one borough in 1546. It was the most populous borough in Wales in the 16th–18th centuries, described by William Camden as "chief citie of the country". Growth stagnated by the mid-19th century as new settlements developed in the South Wales Coalfield.
Moridunum (Carmarthen)
Black Book of Carmarthen
When Britannia was a Roman province, Carmarthen was the civitas capital of the Demetae tribe, known as Moridunum ("Sea Fort"). It is possibly the oldest town in Wales, recorded by Ptolemy and in the Antonine Itinerary. The Roman fort is believed to date from about AD 75. A Roman coin hoard was found nearby in 2006. Near the fort is one of seven surviving Roman amphitheatres in Britain and only two in Roman Wales (the other being at Isca Augusta, Roman Caerleon). Excavated in 1968, the Carmarthen fort has an arena of 50 by 30 yards (about 46 by 27 metres); the cavea (seating area) is 100 by 73 yards (92 by 67 metres). Veprauskas has argued for identifying it as the Cair Guorthigirn ("Fort Vortigern") listed by Nennius among the 28 cities of Britain in his History of the Britons. Evidence of the early Roman town has been investigated for several years, revealing urban sites likely to date from the 2nd century.
During the Middle Ages, the settlement then known as Llanteulyddog ('St Teulyddog's) accounted one of the seven principal sees (Cantrefi) in Dyfed. The strategic importance of Carmarthen caused the Norman William fitz Baldwin to build a castle there, probably about 1094. The current castle site is known to have been occupied since 1105.