In 1142, William, Earl of Lincoln was supposedly granted, by Stephen, a Royal licence to crenellate Gainsborough (Thonock Castle Hills)

"libere et quiete tenendum omnibus liberis consuetudinibus cum quibus aliquis comes Anglie tenet castella sua"

Although this document has been considered by some as a licence to crenellate the current opinion rejects this as a licence to crenellate.

Supposedly a retrospective licence, although Round writes this a royal confirmation of William's possession of the castle. Not, in a meaningful sense, a licence to crenellate although has been called this by some.

Original source is

• Great Coucher, Vol2 fol. 445

(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;

• King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol1 p266n12
  Round, J.H., 1892, Geoffrey de Mandeville (Oxford) p159-60 [citing the Great Coucher Vol2 fol. 445]

More details about licences to crenellate can be found here.

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