Bishop Robert (1121-1159) introduced the canons-regular of St. Augustine in 1144, and these gradually absorbed many of the Culdees into their community. It was during this time also that St. Rule's was built. Dr. Joseph Robertson says of it:--"The little Romanesque church and square tower at St. Andrews, which bear the name of St. Rule, have, so far as we know, no prototype in the south.... No one acquainted with the progress of architecture will have much difficulty in identifying the building with the small 'basilica' reared by Bishop Robert, an English canon-regular of the order of St. Augustine, between the years 1127 and 1144."[36] The Pictish Chronicle states that Robert was elected Bishop in the reign of Alexander I., but was not consecrated till the reign of David I. in 1138; that, after his consecration by Thurstan, Archbishop of York, he expended on this work one-seventh of the altar dues which fell to him, reserving them for his own use. "But inasmuch as the outlay was small, the building made correspondingly small progress, until, by the Divine favour, and the influence of the King, offerings flowed in, and the work went on apace. The basilica was thus founded and in great part constructed."[37] What now remains of this building consists of a square tower, 112 feet high, and an oblong chamber. Discussion has arisen as to whether there ever was a nave, and in favour of the positive view it is urged that marks of three successive roofs may be seen on the tower-wall, and that the seals of the church, dated 1204 and 1214, show a nave and chancel. Eminent authorities take this view. Sir Gilbert Scott thinks that the large size of the western arch, and the mark of the roof on the tower, suggest a nave;[38] while later authorities, recalling that this church was once a cathedral, as well as the church of a monastery, and served the purpose of a parish church, hold it as more than probable that it must have been a larger building than the simple oblong chamber to the east of the tower which now survives.[39] The architecture corresponds with the period of Bishop Robert,[40] so that there is more than probability in averring that St. Rule's was the cathedral built by this bishop, and took the place of an earlier Celtic church, founded by Bishop Acca. The square tower of St. Regulus was probably designed to fulfil the same purposes as the Round Towers of Abernethy and Brechin: (1) to serve as a belfry; (2) to be a keep or place of strength in which the sacred utensils, books, relics, and other valuables were deposited, and into which the ecclesiastics could retire for security in case of sudden predatory attack; (3) when occasion required, to be a beacon or watch-tower.[41]