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].