In 1353 Oct 4, Thomas de Musgrave was granted, by Edward III, (In year 26 of his reign) a Royal licence to crenellate Harcla (Hartley Castle)

"Licence for Thomas de Musgrave to crenellate the dwelling-place of his manor (mansum manerii) of Harcla, situated near the march of Scotland, which has been often burned and destroyed by the Scots in times past. (Harcla quod prope Marchiam Scociae situatur et per Scotos inimicos nostros saepius ante haec tempora combustum extitit et destructum)"

Granted at Westminster, by King.

Thomas de Musgrave received a licence to crenellate in 1353 because it had frequently in the past been burnt by the Scots.

Original source is

• Calendar of Patent Rolls (1350-54) p493

(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, 1996, Greater Medieval Houses Vol1 (Cambridge) p263
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol2 p496n10
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p416

More details about licences to crenellate can be found here.

Please let me know if you see any errors, can add information or can otherwise help to improve this resource. Contact me