Chapter 17. The cycle of Easter. 10. After the completion of this [95-year cycle][313] a return must be made to the beginning. In ancient times the church used to celebrate Easter on the 14th of the moon at the same time as the Jews, whatever day it came on; this way of celebrating the holy Fathers forbade at the council of Nicaea, giving directions to make inquiry not only for the Easter moon and month, but also to observe the day of the resurrection of the Lord, and because of this they extended Easter from the 14th of the moon to the 21st, in order that the _dies Dominicus_ might not be left out. [313] This passage is preceded by a table indicating the date of Easter for 95 years (627–721). It is clear that although Isidore was not acquainted with the plan of Dionysius Exiguus to institute the Christian era, he was acquainted with the essentials of his Easter table. Dionysius had given the dates for Easter in five 19-year cycles, dating from 525; in Isidore this is continued for the years 627 to 721. Isidore’s table consists merely of parallel columns of the days of the month and corresponding days of the moon on which Easter fell. Each date is marked C or E, abbreviations for _communis annus_ and _embolismus_ which describe respectively the year of twelve and that of thirteen lunar months in use in the Hebrew chronology. A further abbreviation, B, stands opposite each fourth year, to mark the leap-years. The years are not numbered according to any era, and the assignment of dates, 627–721, is inferred from the dates given for Easter. See Ideler, _Chronologie_, vol. ii, p. 290 (Berlin, 1826). Isidore does not make it plain that he understood the mathematics of the computation of Easter. It is of interest that in 643 the fourth synod of Toledo passed an enactment to secure a common observance of Easter throughout the Spanish churches, no doubt according to this Easter-table. See Gams, _Die Kirchengeschichte von Spanien_ (Regensburg, 1874), vol. ii, part 2, p. 94. 12. The eve of Easter is spent in watching because of the coming of our King and God, that the time of the resurrection may find us not sleeping but waking. And the reason for this night is a double one, either because he received life at that time when he suffered, or because he is to come for judgment at the same hour at which he arose. 13. And we celebrate Easter in such a way as not merely to call to memory the death and resurrection of Christ but also to consider the rest that is told about him with reference to its mystic meaning (_ad sacramentorum significationem_).