In 1343 Aug 21, Johannes de Norwico (Sir John de Norwyc) was granted, by Edward III, (In year 17 of his reign) a Royal licence to crenellate Metyngham (Mettingham Castle)

"Licence for John de Norwico to crenellate the dwelling-places of his manors (mansum manerii) of Metyngham, co. Suffolk, and Blakworth and Lyng, co. Norfolk."

Granted at Westminster, by privy seal.

Licence to crenellate granted to Sir John Norwich in 1343 for Blakworth, Lyng and Metyngham.

Original source is

• Calendar of Patent Rolls (1343-45) p106

(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;

• Anthony Verduyn, ‘Norwich, John, first Lord Norwich (c.1299–1362)’, Oxford Dictionary of National Biography, Oxford University Press, 2004 [http://www.oxforddnb.com/view/article/20361, accessed 27 Dec 2007]
  King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol2 p462n15
  Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol3 pt2 p413

John Norwich (c. 1299-1362)

John Norwich (c. 1299-1362), son of Sir Walter Norwich - chief baron of the exchequer and treasurer to Edward II, from a relatively modest background; knighted in 1320 with the aid of a gift of £100 from the king's wardrobe; held many military positions; eventual personally summoned to parliament in 1360 and became a peer of the realm.
Norwich returned to England but remained on active service in the years that followed. He was rewarded with a pension in November 1339, which was increased in value to £40 per annum in April 1340. In 1343 he gained a licence to crenellate his properties in Mettingham, Suffolk, and Blackworth and Lyng, both in Norfolk. Norwich served with Henry of Grosmont, earl of Lancaster (d. 1361), in the French campaigns of 1345–7... the castle at Mettingham, Suffolk. The tall gatehouse built by Norwich to show his wealth and power, and which later formed part of the home of his religious foundation, still survives. It is a monument to a family which, during Norwich's own lifetime, had sought to conceal its origins by fabricating a pedigree tracing its ancestry back to a fictitious companion of William the Conqueror. (Verduyn)

Biographical source include;

• Anthony Verduyn, ‘Norwich, John, first Lord Norwich (c.1299–1362)’, Oxford Dictionary of National Biography, Oxford University Press, 2004 [http://www.oxforddnb.com/view/article/20361, accessed 27 Dec 2007]
  

More details about licences to crenellate can be found here.

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