Carmarthen is the county town of Carmarthenshire and a community in Wales, lying on the River Towy 8 miles (13 km) 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.

The Roman era in the area of modern Wales began in 48 AD, with a military invasion by the imperial governor of Roman Britain. The conquest was completed by 78 AD, and Roman rule endured until the region was abandoned in 383 AD.