It is uncertain if this constitutes a licence to crenellate.
The wording of this licence is;Licence, in consideration of Simon, archbishop of Canterbury,having begun,for the fortifying of the city enclosure, the construction of a new gate in the place of the old one called 'Westgate,' whereon used to be the old parish church of 'St. Cross, Westgate,' which the prior and convent of St. Gregory in the suburb of Canterbury have held to their own uses, the church and gate being razed and the parishioners unprovided with their own parish church, for the alienation in mortmain by Thomas Holt, John Bate, William atte Wode, Robert Plomer,Richard Tanner, Adam Jolif, Thomas Cokkere and Thomas Spile, of a plot of land in the city, held of the king in free burgage, fourteen yards (virgas) four feet long, six yards four feet wide, to the said prior and convent, who have licence to construct thereon a new parish church in honour of St. Cross (as their said old church was), and a churchyard, and to appropriate the same in mortmain.
Granted at Westminster, by privy seal.
Original source is
(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.)
Significant later source are;
More details about licences to crenellate can be found here.
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