Additions : 1974 Gelligaer UDC (partly) Vaynor and Penderyn RDC (Partly)
Arms: Azure a Figure representing Saint Tydvil the Martyr in chief two Crosses patée fitchée all Or.
Motto: 'NID CADARN OND BRODYRDDE' - No strength but in fellowship.
The arms were officially granted on August 17, 1906. The arms were regranted in 1976 and 1996 when the town was enlarged.
The arms simply show the patron saint of the town, Saint Tydfil, who was a martyr (Merthyr in Welsh). Following her death in about AD 450, a church was built where she was martyred and the town grew up around it.
Literature : Image and information provided by Laurence Jones (firstname.lastname@example.org)