It has been supposed by several ecclesiastical historians of repute that the Council of Nicaea expressly authorised the bishop of Alexandria to issue these preparatory notices to the authorities in the various churches of Christendom. The evidence for this opinion is lacking; but certainly, as a matter of fact, the judgment of Alexandria carried great weight. In the West, however, the general practice was that Metropolitans should determine the date, and announce the day to their suffragans. In the sixth century the Council of Orleans (A.D. 541) directs that if the Metropolitan were in doubt he should consult the Apostolic see (Rome), and act in accordance with its decision (can. 1). About one hundred years later it would appear from the fifth canon of the Council of Toledo (A.D. 633) that the Spanish Metropolitan bishops did not receive information as to the date of Easter from any external source. They are directed to enquire among themselves by letter three months before the Epiphany, and make the announcement; and the reason assigned for this canon is that erroneous Easter Tables had caused differences.

To attempt anything like a detailed account of the varieties in the methods adopted for the determination of Easter which held their ground for a time, some in the East, some in the West, would be unsuitable in an introductory work like the present. The extraordinary persistence exhibited by the Celtic Churches of Britain and Ireland in maintaining for a long time their own method of computing Easter against the Roman method introduced by Augustine of Canterbury and his followers, is an important and interesting feature in the history of Christianity in these countries. It is enough here to say that the native Churches were not Quartodecimans (as has sometimes been incorrectly alleged), but were adhering to a cycle which they had received long before the Roman missionaries arrived in Britain[162]. We must here be content with briefly noticing some of the leading features in the history of the change which gradually led up to the adoption of the Nineteen-Year Cycle as modified and propounded by Dionysius Exiguus in the early part of the sixth century.

After the abandonment of the Cycle of Hippolytus there is found in use at Rome an 84-year cycle. In this the date of Easter is believed to have oscillated between March 25 and April 21; and between the fourteenth and twentieth day of the moon. This system, according to the results of recent research, was modified in A.D. 312 and again in A.D. 343. This cycle (still of 84 years) came to be known as the supputatio Romana. Easter could not now fall earlier than the sixteenth, nor later than the twenty-second of the moon, while its date limits were March 22 and April 21. This supputatio, with some modifications, served the bishops of Rome during the fourth and the greater part of the fifth century. The Alexandrians, on the other hand, had about A.D. 277 come to use the more exact Nineteen-Year cycle, with possible Easters between March 22 and April 25, and between the fifteenth and twenty-second of the moon[163].

In the pontificate of Leo the Great the differences which he had with the Church of Alexandria as to the date of Easter caused him to direct his archdeacon, Hilary (who afterwards succeeded to the papal throne), to investigate the whole question. Hilary resorted to the aid of Victorius of Aquitaine, who happened to be then at Rome. Victorius devised, or adopted, a cycle of 532 years, a combination of the lunar cycle of 19 years with the so-called solar cycle of 28 years (19 × 28 = 532). His Easter limits were March 22 and April 24.

The cycle of Victorius met with favourable acceptance, more particularly in Gaul, where it continued in use till nearly the end of the eighth century.

At Rome, whatever may have been the position actually attained by the cycle of Victorius, it and all other devices for determining Easter gave way in the sixth century (A.D. 527) before the Paschal Tables of Dionysius Exiguus. This remarkable person, who came to occupy an eminent place in the science of chronology generally, as well as in the computations necessary for ecclesiastical purposes, was a monk, a Scythian by birth, who settled in a monastery at Rome. It is to him that we owe in chronology the adoption by Western Christendom of what we know as the ‘Christian Era’ and ‘the year of our Lord,’ now in universal use for the dating of the events of history, and of all our documents public and private.

The system of Dionysius was, practically, the adoption of the Nineteen-Year Cycle of the Alexandrians. It fixed the date of the vernal equinox at March 21, placed the Paschal limits at March 22 and April 25, and declared Easter to be the next Sunday after the Paschal full moon. We have here in full the rule which eventually came to prevail everywhere. But its adoption was not immediate in all countries[164].

The space at our disposal will not allow of our treating in detail of the work of the computists, and of the ‘Sunday Letters,’ ‘Epacts,’ and other technical terms which appear in the old Church Kalendars. For these, as well as for such terms as ‘Indiction,’ ‘Lunar Regulars,’ ‘Solar Regulars,’ and ‘Concurrents,’ reference may be made to such books as Sir Harris Nicholas’ Chronology of History, and Giry’s fuller and lucid Manuel de Diplomatique.

The Gregorian Reform.

The defects of the Nineteen-Year Cycle became apparent after some lapse of time. There were two grave sources of error. First, the Kalendar proceeded on the assumption that the solar year consisted of 365¼ days; but the true solar year is 11 minutes and some seconds shorter than the Kalendar year, and the accumulation of this error gradually brought confusion into the system. In one hundred and thirty years the Kalendar will have gained on the true solar year by almost exactly one day. At the date of the Council of Nicaea (A.D. 325) the vernal equinox was placed at March 21, but in the year A.D. 450 the true vernal equinox would be on March 20. In A.D. 585 the equinox would be on March 19; in A.D. 715 on March 18, and so on. And thus it will be seen that in A.D. 1582, when the Kalendar was reformed, the real vernal equinox was about ten days earlier than the March 21 of the Kalendar.