"Pro Mauritio de Gaunt de castro suo de Beverestan.- Rex omnibus ad quoa presentes litere pervenerint, salutem. Sciatis quod concessimus pro nobis et heredibus nostris dilecto et fideli nostro Mauritio de Gaunt et heredibus suis, quod castrum suum quod firmari fecit apud manerium suum Beverestan stet et remaneat inperpetuum ibidem prout nunc firmatum est. In cujus etc. fieri fecimus. Teste rege, apud Sanctum Neotum"
Granted at St. Neots, by King.
King writes "This is plainly an ex post facto licence, for a pre-existing castle."
Original source is
(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;
More details about licences to crenellate can be found here.
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