The Gatehouse website record of a licence to crenellate for Harswell, Everingham granted on 1303 Oct 20

In 1303 Oct 20, Gerardus Salvayn (Salvayan) was granted, by Edward I, (In year 31 of his reign) a Royal licence to crenellate Herssewell in Spaldingmor. (Harswell, Everingham)

Granted at Dundee. Grant by privy seal.

Original source is;

Lyte, H.C. Maxwell (ed), 1898, Calendar of Patent Rolls (1301-7) p. 160 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;

Emery, Anthony, 1996, Greater Medieval Houses Vol. 1 (Cambridge) p. 421
Turner, T.H. and Parker, J.H., 1859, Some account of Domestic Architecture in England (Oxford) Vol. 3 part 2 p. 404 online copy

Salveyn, Sir Gerard (d. 1319/20)

Salveyn was, however, more than merely a Yorkshire county administrator. He was employed on missions overseas by both Edward I and Edward II, for example in September 1304, May 1310, and March 1311. He was one of the royal officials whom the ordainers removed from office and access to the king in 1311; their animosity probably reflects the fact that Salveyn had by this time became a household banneret, and as such was close to the king, since it probably fell to him to escort Piers Gaveston to the continent late in 1311, and to bring him back to the king early in the following year. (Kingsford)

Salveyn, Sir Gerard (d. 1319/20) served on a number of judicial commission, became sheriff of Yorkshire in 1311 and serve both Edward I and Edward II on overseas missions. However this licence granted relatively early in his career (although he was probably at least in his thirties - an adult son is mentioned in 1311) when he was mainly serving as a soldier and tax collector. The family seat seems to have been North Duffield, near Selby were a manor house was mentioned in 1320, although nothing survives. Gatehouse has not been able to trace the previous holding of Harswell. The licence may be to confirm ownership.

Biographical source include;

C. L. Kingsford, 2004, ‘Salveyn, Sir Gerard (d. 1319/20)’, rev. Helen M. Jewell, Oxford Dictionary of National Biography (Oxford University Press) online copy (subscription may be needed)