Ely was now raised to the dignity of a bishopric, the revenues of the abbot being used for the endowment of the see, and henceforth the prior was the head of the monastery. The building of the church proceeded gradually. The nave was growing by degrees during the twelfth century, and Bishop Riddell (1174-1189), by his energy, did much towards its completion and that of the great west tower. The isle was much disturbed during the troublous time of Stephen's reign, and the bishop took the part of the enemies of the king, who exacted heavy fines from the prelate and his monks. Bishop Eustace (1198-1215) accomplished much, and erected the beautiful Galilee Porch. In 1235 the building of the noble presbytery was begun by Bishop Northwold (1229-1254), and here, in the presence of King Henry III. and his court, the shrines of the founders and of three other abbesses were removed, and the whole church in ground plan completed as we see it to-day. [Illustration ARM OF ABBOT'S CHAIR] Having finished their church, the monks turned their attention to their domestic buildings, and to the Lady Chapel, which stands here in an unusual position. It was erected by Alan de Walsingham (the sub-prior) in 1321, and finished in 1349. In 1322 a sad calamity happened--the central tower fell, and caused much destruction. But the catastrophe called forth the constructive genius of Alan de Walsingham, a prince among architects, who built the beautiful octagon and lantern tower, which add so much grace and beauty to the building. The superb Lady Chapel, with its marvellous sculptured work, the sub-structure of St. Etheldreda's shrine, and Prior Crauden's Chapel--a perfect gem of beauty and originality--are all Alan de Walsingham's work. The monks elected this great builder Bishop of Ely, but the Pope refused to ratify the election. He is admirably described on his tomb as the _Flos Operatorum_, or "flower of craftsmen." [Illustration WEST TOWER FROM DEANERY GARDENS] In this period Decorated windows were inserted in the triforium of the presbytery, the outside walls being raised for this purpose, and flying buttresses added. The Cathedral then appeared externally much as we see it to-day. The Perpendicular style finds few examples in Ely except in some of the smaller chapels and one or two windows. [Illustration The Assumption of the Blessed Virgin Mary Lady Chapel.]