The discussion, as to the proper time of observing Easter, which had occupied the doctors of the Council of Nice in the fourth century, was raised in Ireland and in Britain early in the sixth, and complete uniformity was not established till far on in the eighth. It occupied the thoughts of several generations of the chief men of the Irish Church, and some of their arguments still fortunately survive, to attest their learning and tolerance, as well as their zeal. St. Patrick had introduced in the fifth century the computation of time then observed in Gaul, and to this custom many of the Irish doctors rigidly adhered, long after the rest of Christendom had agreed to adopt the Alexandrian computation. Great names were found on both sides of the controversy: Columbanus, Finian, and Aidan, for adhering exactly to the rule of St. Patrick; Cummian, the White, Laserian and Adamnan, in favour of strict agreement with Rome and the East. Monks of the same Monastery and Bishops of the same Province maintained opposite opinions with equal ardour and mutual charity. It was a question of discipline, not a matter of faith; but it involved a still greater question, whether national churches were to plead the inviolability of their local usages, even on points of discipline, against the sense and decision of the Universal Church. In the year of our Lord 630, the Synod of Leighlin was held, under the shelter of the ridge of Leinster, and the presidency of St. Laserian. Both parties at length agreed to send deputies to Rome, as "children to their mother," to learn her decision. Three years later, that decision was made known, and the midland and southern dioceses at once adopted it. The northern churches, however, still held out, under the lead of Armagh and the influence of Iona, nor was it till a century later that this scandal of celebrating Easter on two different days in the same church was entirely removed. In justification of the Roman rule, St. Cummian, about the middle of the seventh century, wrote his famous epistle to Segenius, Abbot of Iona, of the ability and learning of which all modern writers from Archbishop Usher to Thomas Moore, speak in terms of the highest praise. It is one of the few remaining documents of that controversy. A less vital question of discipline arose about the tonsure. The Irish shaved the head in a semicircle from temple to temple, while the Latin usage was to shave the crown, leaving an external circle of hair to typify the crown of thorns. At the conference of Whitby (A.D. 664) this was one of the subjects of discussion between the clergy of Iona, and those who followed the Roman method—but it never assumed the importance of the Easter controversy.