In 1337 Aug 12, Johannes de Coloygne (John Cologne) was granted, by Edward III, (In year 11 of his reign) a Royal licence to crenellate Cornhill (Cornhill, London)

"dilectus vallettus noster ... domos suas super Cornhill infra civitatem nostram"

Granted at Tower of London, by privy seal.

John de Coloygne seems to have been a merchant who dealt, at least in part, in pearls since a dispute over his will, in 1363, was about an outstanding debt for 11,500 pearls. This amount of wealth suggest the licence had some practical consideration.

Original source is

• Calendar of Patent Rolls (1334-38) p505

(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;

• Emery, Anthony, 2006, Greater Medieval Houses Vol3 (Cambridge) p439
  Coulson, C., 1995, 'Battlements and the Bourgeoisie: Municipal Status and the Apparatus of Urban Defence' in Church, Stephen (ed), Medieval Knighthood Vol. 5 (Boydell) p194n297
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p411

More details about licences to crenellate can be found here.

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