Llantrisant lies within a saddle between two hills on the escarpment marking the southern edge of the Glamorgan uplands. The parish church (NPRN 14034) was probably built in the twelfth century and the present castle (NPRN 93041) in 1246 following the annexation of upland Penychen by the lords of Glamorgan. This was the administrative centre for the commotes of Meisgyn and Glynrhondda.
The borough was probably founded with the castle and is first mentioned in 1262. It was several times devastated in the wars and riots in the closing years of the thirteenth century and the earlier part of the fourteenth century. In 1307 there were 150 burgages or house plots and there may have been more than 200 in 1349. Charters were granted in 1346 and 1424. The borough had declined by the fifteenth century and over sixty burgages had been abandoned by 1492. It further declined until its abolition as a 'dissolute and venal' borough in 1883.
Some indications of the layout of the medieval borough can be discerned on the 1st edition OS County series (Glamorgan. XXXVI.13 1877). There appear to be infilled market places at either end of High Street on the north side of the castle and church. The Bullring remains open. The eighteenth century Guildhall remains (NPRN 31911) although the attached market had been replaced by the Police Station by the time of the 2nd edition of 1899.

Source: RCAHMW Glamorgan Inventory III.1b The Later Castles (2000), 186-9

John Wiles 12.02.08