In 1510 July 6, Edward, Duke of Buckingham (Edward Stafford) was granted, by Henry VIII, (In year 2 of his reign) a Royal licence to crenellate Thournebury (Thornbury Castle)

"Licence to impark 1,000 acres of land in the parish of Thournebury, Glouc.; also to castellate his manor or mansion of Thournebury.
to fortify, crenellate, and embattle his manor or mansion house there with walls of stone or lime and to make the building a fortilace or castle"

Granted at Windsor Castle, by privy seal.

Original source is

• Letters and Papers, Foreign and Domestic, of the Reign of Henry VIII Vol1 p172 No1157

(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;

• Emery, Anthony, 2006, Greater Medieval Houses Vol3 (Cambridge) p212
  Guy, Neil, 2005-6, 'Thornbury Castle' Castle Studies Group Journal Vol 19 p207
  Hawkyard, A.D.K., 1977, 'Thornbury Castle' Transactions of the Bristol and Gloucestershire Archaeological Society Vol95 p51-58

More details about licences to crenellate can be found here.

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