William de Mandeville, Earl of Essex, like his deceased kinsman, espoused the cause of the barons and stoutly maintained it, even after the decease of King John, being one of those who then assisted Lewis of France in the siege of Berkhamstead Castle, occupied by the king's forced. A sally having been made, however, from the garrison, much of the baggage of the besiegers was captured and, amongst other things, the banner of the Earl William. His lordship seems to have made his peace soon after, for we find him engaged in the Welsh wars. He d. in the flower of his age, 25 December, 1227, and, as he left no issue, the Earldom of Essex devolved upon his sister, Mary, Countess of Hereford, while the lands which he inherited passed to his half-brother, John FitzPiers. [Sir Bernard Burke, Dormant, Abeyant, Forfeited and Extinct Peerages, Burke's Peerage, Ltd., London, England, 1883, p. 353, Mandeville, Earls of Essex]