After the Council of Nicaea, although the Quartodeciman practice lingered on among unorthodox sectaries, the differences among Catholics were in the main confined to such questions as, When was the equinox? and What Tables should be used for predicting the Sunday which should be observed as Easter Day? The Synod of Antioch in A.D. 341 (can. 1) could now make bold to advance a step beyond the Oecumenical Council, and enacted a canon pronouncing excommunication against any who acted contrary to the command of the great and holy Synod assembled at Nicaea regarding the Pascha[160]. In principle the Church was united; but there were differences in the application of the principle. In A.D. 444, and eleven years later, in A.D. 455, Pope Leo the Great was in perplexity as to the day upon which Easter should be kept. In A.D. 444 he wrote to Cyril of Alexandria on the subject. The answer he received was that the proper day was not March 26 (as the Latins would make it) but April 23. In A.D. 455 Leo was much moved by finding that the Alexandrian computists had given April 24 for Easter Day, while those at Rome had assigned the festival to April 17, a week earlier. The matter seemed to him of sufficient importance to justify his writing to Marcianus, Emperor of the East, whom he now besought to intervene, and direct the Alexandrians not to name April 24, declaring that so late a date was beyond the ancient Paschal limits. Leo also wrote on the same subject to the learned and once beautiful Eudocia Augusta, who, though now spending her old age in retirement and devotion at Jerusalem, was not without influence in church affairs. The Emperor had enquiries made among certain bishops of the East and communicated with the Alexandrians. The result was that the observance of April 24 was reaffirmed, and the bishop of Rome reluctantly submitted for the sake of peace[161]. The account of the matter lies in the fact that while the Alexandrians had long before adopted the Paschal limits that still continue to rule our Easter, that is, from March 22 to April 25, the Latins, though at this date accepting the prior limit, hesitated as to the later, because the Easter Tables then in use among them had placed the later Paschal limit on April 23. The position of authority conceded to the Church of Alexandria on the question as to the date of the Pascha was due to the acknowledged learning and skill of the astronomers and mathematicians of that city in matters of chronology and the computation of time. It was the practice of the bishop of Alexandria, as early at least as the middle of the third century, to issue what were styled ‘Festal Letters’ or, at a later date, ‘Paschal Letters,’ commonly of the nature of a homily on the religious lessons of the Paschal season, with an announcement as to the date of the next Pascha. These letters were commonly issued by the bishop a year in advance, and were sent by special messengers to his comprovincial bishops.