In 1302 Feb 16, Willielmus de Hamelton, decanus ecclesiae Beati Petri Ebor (William of Hambleton) was granted, by Edward I, (In year 30 of his reign) a Royal licence to crenellate Ebor (York Deanery)

"mansum suum Cimeterio ejusdem ecclesiae contiguum muro de perta et calce firmare et kernellare"

Granted at Roxburgh, by privy seal.

Presumably this is William of Hambleton who became Royal Chancellor in 1305.

Original source is

• Calendar of Patent Rolls (1301-7) p19

(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;

• Coulson, C., 1982, 'Hierarchism in Conventual Crenellation' Medieval Archaeology Vol26 p93
  Tillott, P.M. (ed), 1961, 'The twelfth and thirteenth centuries: The aspect of the city', VCH Yorkshire: the City of York p51-4
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p404

More details about licences to crenellate can be found here.

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