In 1271 June 9, Willielmus Belet (William Belet) was granted, by Henry III, (In year 55 of his reign) a Royal licence to crenellate Marham (Marham Castle)

"Licence to William Belet and his heirs to crenellate his house (domum suam) of Marham, co. Norfolk."

Granted at Westminster,

See Coulson (2003) pp131-133 for details of the licencing and the reasons for this minor site being called a castle. "The work was alleged to injurious to Norwich castle. Local friction, and possibly the role of the Isle of Ely and of Cambridge in 1266-7, was the cause. The licence was evidently upheld since nothing was done over this very minor castellum.

Original source is

• Calendar of Patent Rolls (1266-72) p540

(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;

• Charles Coulson, 2003, Castles in Medieval Society (OUP; Oxford) p131-3, 135, 140, 173, 324
  Coulson, C., 1994, 'Freedom to Crenellate by Licence - An Historiographical Revision' Nottingham Medieval Studies Vol38 p94, 126n120
  King, D.J.C., 1983, Castellarium Anglicanum (New York) Vol2 p313n22a
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p403

More details about licences to crenellate can be found here.

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