In Wykeham's twenty-third year Edward III came to Winchester, and he, having heard of the clever young architect, wished to test his skill in the warfare then being waged against Scotland and France, and particularly in the new fortifications of Calais. On taking service with the King, plain William Wykeham became Sir William de Wykeham, and as Surveyor of Works he superintended such buildings as St. Stephen's Chapel, Westminster, and the castles of Dover and Queensborough. In 1356 he was in charge of Windsor Castle, which, as his birthplace, Edward wished to beautify by many additions. It has been said that the Round Tower Wykeham built at Windsor made the fortune of its designer. We now find Wykeham Warden of all the royal castles, and sub-dean of the church of St. Martins-le-Grand, on the site of which is the General Post Office; and as a public notary he was present at the signing of the Treaty of Bretigny.

Possibly owing to the dearth of clergy caused by the Black Death, Wykeham, after the laying-on of hands by his old master, Bishop Edington, became an acolyte in the December of 1361, a sub-deacon in the March following, and priest in the June of 1362. A few years later, when Edington was laid to rest within his cathedral, a sharp controversy arose between the King and the Pope as to who should succeed. The differences, which need not be discussed here, being eventually settled to the satisfaction of both parties, Wykeham was offered the vacant see, when he said to the King:

"Sire, I am unworthy, but wherein I am wanting myself, that will I supply by a brood of more scholars than all the prelates of England ever showed".

And how worthily he fulfilled his promise is a matter of history.

To quote the authors of Historic Winchester:

"There was a great stir in the old city when the day of Wykeham's enthronement arrived. It was the 9th of July, and the town would be looking especially beautiful in its bower of trees; an outrider had announced the bishop before he entered the city, probably by the north gate, and either here or at the entrance to the close he was met by the Archdeacon of Northampton, William Athey by name, who was commissioned to enthrone him: having saluted, the Archdeacon alighted from his palfrey, which according to the custom at that time was with all its trappings taken possession of by this ecclesiastic.... The bishop's robing most probably took place at the priory close by, from whence the procession, forming in the cloisters under the direction of Hugo de Basyng, prior of St. Swithun's, would pass to the west door, where it would be joined by the heads of the other monasteries in and near Winchester—Thomas de Pechy, Abbot of Hyde, holding highest rank amongst them. Next would follow long lines of monks clad in their robes of brown, black, white, or grey, according to their order, and then many a layman, gathered in from the country round to honour both Church and State on this occasion. The great procession, gorgeous with embroidered cope and many a rich vestment, with episcopal staff and crozier both of prior and abbot carried aloft, must have formed an imposing spectacle as it filed up the long nave of the cathedral, thronged, doubtless, to overflowing by many citizens—for unusual interest would be evinced by Winchester in this enthronement of one long known to them, now Chancellor of England and certainly, next to the King and Archbishop, the greatest man in the country."

As bishop, Wykeham found plenty to do, apart from his ecclesiastical duties, in repairing his various palaces, and in housing the predecessors of his Winchester scholars in a house on St. Giles's Hill, until such time as he could give them fitting buildings and a chapel of their own. But before Wykeham could see his schemes take an architectural form, he was to suffer the loss of royal favour owing to the death of the Black Prince and the rise into power of his enemy, John of Gaunt. The bishop was charged with the misappropriation of a small sum of money, and, judgment being given against him, the temporalities of the see of Winchester were seized, and he was forbidden to come within twenty miles of the Court. He retired to Waverley Abbey, of which some picturesque ruins remain, near Farnham; and although on the King's jubilee pardon was granted to all offenders, a special exception was made in the case of "Sire William de Wykeham".

WYKEHAM'S CHANTRY