In 1378 March 20, Prior et Conventus ecclesiae cathedralis beatae Mariae Wygorn was granted, by Richard II, (In year 1 of his reign) a Confirmation licence to crenellate Wygorn (Worcester Cathedral Priory)

"Inspeximus and confirmation, in favour of the prior and convent of Worcester, of the following:
1. A charter, dated York,7 June, 9 Edward III. [Charter Roll, 9 Edward III., No. 49 ] inspecting and confirming (1) A charter, dated Westminster,19 February, 6 Edward II., and (2) A charter dated Westminster, 3 February, 6 Edward II. [Charter Roll, 6 Edward III., Nos25 and 27], both inspecting and confirming divers early charters, viz. of Edgar, Edward the Confessor, William the Conqueror, HenryII., John and HenryIII.
2. Letters patent, dated 8 July, 29 Edward III., inspecting and confirming a charter, dated 2 April, 40 Henry III.
3. Letters patent, dated 20 February,43 Edward III., being a licence to crenellate their priory. [Monasticon: Vol. i., p. 593]."

Granted at Westminster, by For 10 marks paid in the hanaper.

The abbey paid 10 marks for the licence of 1369 and other charters to be confirmed in the first year of Richard II reign.
It appears that the great gate house of the abbey, the Edgar Tower, was finished by this time but the watergate and the riverside precinct wall may well date from 1378.

Original source is

• Calendar of Patent Rolls (1377-81) p165

(In fact, the original source given is usually a transcription/translation of what are precious medieval documents not readily availably. It should be noted that these transcription/translations often date to the nineteenth or early twentieth centuries and that unwitting bias of transcribers may affect the translation. Care should also be taken to avoid giving modern meaning to the medieval use of certain stock words and terms.)

More details about licences to crenellate can be found here.

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