In 1257 Dec 12, Adomar Winton, the king's brother (Aylmer de Lusignan) was granted, by Henry III, (In year 42 of his reign) a Royal licence to crenellate insulam de Portand (Portland [Rufus Castle])

"electus possit kernellare...insulam de
Licence for Aymer, [bishop] elect of Winchester, the king's brother, to strengthen the island of Portand, with stone and lime and to crencllate it like a castle, as he shall think most expedient"

Granted at Westminster, by King.

King writes "to Aylmer de Lusignan, Bishop-elect of Winchester. The terms of this licence are extremely vague; Aylmer was permitted to crenellate the island or make a castle there at his complete discretion. The nature of the problem seems not to have been considered at this stage." It is generally presumed that Rufus castle is the site of any work that may have resulted from this licence.

Original source is

• Calendar of Patent Rolls (1247-58) p607

(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;

• Thompson, M.W., 1998, Medieval bishops' houses in England and Wales (Aldershot: Ashgate Publishing) p167
  Coulson, C., 1994, 'Freedom to Crenellate by Licence - An Historiographical Revision' Nottingham Medieval Studies Vol38 p131
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol1 p132n32
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p402

More details about licences to crenellate can be found here.

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