A petition by Gilbert de Clare, Earl of Gloucester, undated but c. 1266, asking for murage for Kilkenny asked 'that the murage of Thomastown granted by the justiciar of Ireland be revoked since it is to the prejudice of the Earl's men'. (Nat. Arch.)
the earliest known reference to murage (CDI I 732) is rather equivocal, bothas regards date and outcome, but it shows intention to wall as early as the mid-13th century which is earlier than usual for the smaller, no-royal Irish towns. The document is dated to 'early' in the reign of Henry III (1216-72) but internal evidence suggests a date probably after 1248 (vide Kilkenny - Bradley 1975-6, 89). It was a request to revoke the murage of Thomastown 'granted by the Justiciary of Ireland' on the basis that it was prejudicial to that of Kilkenny. (Thomas)
From Thomas it is clear the National Archive document and that calendared by Sweetman are the same. The NA date this as 1266 on the bases of a murage grant given to Kilkenny of that date, which mentions G. Earl of Gloucester and is pretty clearly a response to his petition. The 1266 date is unsatisfactory, since the details of the grant do not fit with the petition. The suggestion that earl of Gloucester was Gilbert seems to be to fit with this 1266 date; his father Richard, also earl of Gloucester, had inherited the lordship of Kilkenny from his mother, Isabel Marshall, on her death in 1240. Irish records have been split over several archives, some of which have been destroyed, so there is a distinct possibility that the resulting grant is not calendared or otherwise known.
Munby and Tyler date this to c. 1248, presumably based on Bradley. This date is not unreasonable although a date of 1252-3, when Richard was in Ireland, may be worth consideration.