In 1438, Joan, widow of Gwilym ap Gruffudd was possibly granted, by Henry VI, a Royal licence to crenellate (Penrhyn Castle)

There is insufficient evidence to be certain about this possible licence to crenellate.

Significant later source are;

• Pettifer, Adrian, 2000, Welsh Castles, A Guide by Counties (Boydell Press) p36
  Salter, Mike, 1997, The Castles of North Wales (Malvern) p48

More details about licences to crenellate can be found here.

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