Caerfyrddin

The Welsh name for the city of Carmarthen, seat of Dyfed county, Wales.

The name comes from caer and myrddin. Caer means a fort--like the Gaelic dun in Dunedin (Edinburgh), and is a common element of placenames in Welsh.

Myrddin is more difficult. Once, people believed it derived from the man Myrddin (who of course is Merlin), and so etymologized it as meaning "Myrddin's Fort." However, myrddin actually derives from the old Roman name for the city, Maridunum, which in early British² means "sea fort," which is appropriate, as the city sits on the coast.

Hence, Myrddin's name is thought to mean "a man from Carmarthen," and not the other way around. This is possible, as in the older texts, there seems to be two Myrddins, Myrddin Emrys and Myrddin Wyllt--Emrys from Carmarthen and Wyllt from Carmarthen?

The city is best known outside of Wales as the origin of Llyfyr Ddu Caerfyrddin--the Black Book of Carmarthen.

2. I say "British," meaning a mix of old Welsh and Latin. Maridunum could be Welsh/Celtic, or it could be a Latinization of Welsh. Either way, mari comes from "mare" in Latin, or "môr" in Welsh (though this is modern Welsh), and "dunum" means fort in Celtic languages, which can be seen in the modern Welsh dinas, meaning a city.