The Gatehouse website record of a licence to crenellate for Bygrave House granted on 1386 Oct 31

Original source is;

Lyte, H.C. Maxwell (ed), 1900, Calendar of Patent Rolls (1385-89) p. 235 online copy

(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. Licentia is best translated as 'freedom to' not 'permission'.)

Significant later sources are;

King, D.J.C., 1983, Castellarium Anglicanum (London: Kraus) Vol. 1 p. 222n17a
Page, Wm (ed), 1912, VCH Hertfordshire Vol. 3 p. 215 online copy
Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol. 3 part 2 p. 419 online copy

Sir John Thornbury, (d.c. 1397)

Sir John Thornbury, (d.c. 1397) a captain of papal mercenaries in Emilia in 1374. Appears to have made a considerable amount of money from his mercenary career (entries in the Calendar of plea and memoranda rolls of the city of London, record his wife, as his executrix, obtaining 2000 marks from foreign merchants)

In 1383 Alexander de Walden 'sold Bygrave to Sir John Thornbury, the 'king's knight,' and one of his justices of the peace in Hertfordshire. In 1386 Thornbury had licence to crenellate his two houses within the manor of Bygrave. He served as commissioner of array in the county in 1392 when it was feared that the expiration of the truce with France might be followed by invasion.' (VCH)

From before 1380 he began to settle and purchased estates in Hertfordshire. He became a retainer of John of Gaunt in 1380 and obtained royal patent letters exempting him from a wide range of duties in 1381, although he chose to serve as MP for Hertfordshire in 1382, 1385 and 1390. (Roskell)

A mercenary soldier, of obscure background, who made good and then spent his later years establishing himself as a member of the gentry, equipped with all the paraphenial, including crenellated house and a seat in the commons.

Biographical source include;

Roskell, J.S., Clark, Linda and Rawcliffe, Carole, 1992, The House of Commons 1386-1421 (History of Parliament Trust) Vol. 4 p. 591-3

More information about licences to crenellate can be found here.

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