It would be reasonable to assume that a Guildhall has stood on the same site adjacent to Llantrisant Castle since the year it received borough status in 1346 if not earlier.
The Castle was fortified in 1246 with two towers and a small enclosure, which presumably also incorporated the medieval court house, or Guildhall of the period, which means it may even date from the mid 13th century.
It was this area that they were largely responsible for administrating the borough of Meisgyn and Glynrhondda and as the seat of local government the Guildhall was a building of immense power and prestige.
The Court Leet was held at the Guildhall from the presentment of the first Charter in 1346 but we can only rely on the Confirmation Charter of 1424 by Richard Beachamp, Earl of Warwick and Lord le Despenser, Lord of Glamorgan for the extent of its power.
The Charter sets out a bill of rights for the “burgesses” (Freemen) of the borough stating “They may for a guild amongst themselves, for their own profit”. It goes on to state that “The constable may hold hundred courts, monthly of pleas and complaints, except the pleas of the crown and certain others.”
That in itself implies the “hundred court” was to be held regularly, therefore suggesting that a building would have been necessary to fulfill this functions and others relating to the Charter. The Charter had a commercial aspect, emphasizing the freedom of burgesses to trade throughout the Despensers estates without payment of tolls.
A merchant guild was to be established and the trades of the neighbourhood to be polarized in the market place so that visiting merchants could buy and sell there on market and fair days, paying tolls for the privilege.