King writes "A licence was not normally required in this part of the country, but the owner, Fulk fitz Warin II, was a suspect character; he was permitted to build (firmare) his castle, but next year the King is found giving orders that the castle was not to be stronger, or otherwise built, than for defence against the Welsh; if it could not be defended against them, it was to be returned to the state it had been in before the war; i.e. presumably that of a defenceless earthwork (Rot. Lit. Claus., i, 520b)"
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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