An enquiry in 1267 adjudged property of “Philippus olim comes Bolonie et...Matildis” to “Matheus comes Domni-Martini, domini Guillelmus de Fienes, Baldoinus de Fienes, Michael de Fienes, Ingerannus de Pinquegniaco et Renaudus de Pinquegniaco, heredes comitisse Matildis Bolonie”. “Willaume chevalier sires de Fienles” approved an exchange of property between Notre-Dame de Licques and “me sire Ingheran de Journi”, for the souls of “mi, de dame Blanche me feme...”, by charter dated 14 Jun 1276.
The Chronique Artésienne records “mesires de Fiennes” among those killed at the battle of Courtrai 11 Jul 1302. 1
Named in the 1296 Inquisition taken following the death of his mother Isabel de Fynes as the right heir of the manor of Wendover.
Chevalier, seigneur of Fiennes and Tingry (Pas-de-Calais), and, in England, of Wendover, Buckinghamshire, Fyfield and Lambourne, Essex, Chokes and Gayton, Northamptonshire, Martock, Somerset, Carshalton and Clapham, Surrey, etc., custodian of the county of Ponthieu, 1279, and, in right of his wife, seigneur of la Suze and Louplande (both in Maine), son and heir....
In 1267 William and his uncles, Michael de Fiennes and Baldwin de Fiennes, chevalier, were assigned part of the goods of their cousin, Mahaut de Dammartin, Countess in Boulogne and Dammartin. He and his brother, Giles, joined the Crusade to the Holy Land in 1270-2 under Lord Edward. The first week of May 1270 he and his father, Enguerrand de Fiennes, Knt., separately ratified the sale of land at Quesnoy de Wailly made by William's uncle, Baldwin de Fiennes, chevalier, to the lepers of du Val. William's name occurs as a knight of the household who attended King Louis IX in his expedition to Tunis in 1270. In 1275 William pledged part of his estates, including Martock, Somerset, to his kinswoman, Eleanor of Castile, wife of King Edward I, when, at his request, she agreed to pay £1000 to Humphrey de Bohun on the latter's marriage to his sister, Maud... In 1275-6 the abbot of Michelney arraigned an assize of novel disseisin against him and others touching common of pasture in Martock, Somerset. In 1276-7 Robert Rudal arraigned an assize of novel disseisin against him and others touching common of pasture in Martock, Somerset. In 1277 he sold a tract of land at l'Aunaie in Morbecque to Marguerite, Countess of Flanders. He was summoned to serve against the Welsh in 1277 and 1282. He held custody of the county of Ponthieu in 1279. In 1282 he conveyed some rights in Fyfield, Essex to Robert Burnell, Bishop of Bath and Wells.... William spent many years beyond the seas, yet was restored to his English lands during the truce of 1299, for which he acted as a hostage in the negotiations between England and France. He was summoned to serve against the Scots in 1300. Due to considerable debts, he conveyed his manor of Clapham, Surrey to Thomas Romayn, Citizen of London; his manor of Carshalton, Surrey to William de Ambesas, Knt.; and his manor of Lambourne, Essex to Robert Burnell, Bishop of Bath and Wells. Sir William de Fiennes was slain with many other magnates at the Battle of Courtrai 11 July 1302. 2