The development the Alexandrian method for determining Julian or Alexandrian calendar dates of Paschal Sunday underwent is nothing less than the mainstream of the history of the computus (i.e. Paschal reckoning) which rose in third century Alexandria (Egypt) to ultimately (in sixteenth century Rome) flow into an astronomically more realistic method for determining Gregorian calendar dates of Easter. In this mainstream there were only two real rapids:
1) first the solid construction (on the basis of at the time recent lunar tables) of the proto Alexandrian lunar cycle and Anatolius’ lunar cycle, being the (lost) Alexandrian Metonic lunar cycle(s) from which the great third century Alexandrian computist Anatolius started in order to construct his famous 19 year Paschal cycle;
2) then the also solid construction (also on the basis of at the time recent lunar tables) of the archetypal Alexandrian lunar cycle, being the (also lost) ante Nicene common archetype of the three well known post Nicene Alexandrian Metonic lunar cycles.
The proto Alexandrian lunar cycle and Anatolius’ lunar cycle were constructed somewhere between AD 250 and 282 inclusive, the as well Metonically structured archetypal Alexandrian lunar cycle was constructed barely half a century later, not long before the first council of Nicaea in AD 325, turning point in the history of Christianity. And so it is not so much because of different moments of construction but because of different sets of computistical principles according to which they were constructed that the latter lunar cycle differs so much from the (mutually equal) former ones. After having reconstructed them, we establish (see Table 8) that:
1) there exists a just not quite perfect ante Nicene 2 day gap between Anatolius’ lunar cycle and the archetypal Alexandrian lunar cycle, the cause of which must be sought exclusively in the transition in Alexandria and beyond from the more Jewish Christian world of the third century to the more Gentile Christian world of the fourth (as a result of which Alexandrian computists went to use the Egyptian lunar calendar much more familiar to them instead of the Alexandrian version of the Jewish lunar calendar);
2) Anatolius’ lunar cycle has de facto limit dates 23 March and 20 April, but the sequence of Paschal dates generated by this lunar cycle according to the old Alexandrian Paschal rule has de facto limit dates 23 March and 26 April;
3) the archetypal Alexandrian lunar cycle is the archetype from which after bishop Athanasius’ death in AD 373 one after another the three well known post Nicene Alexandrian Metonic lunar cycles would be obtained if not by simply adopting it then by simply adapting it by moving its saltus a few years afterward or forward;
4) the three well known post Nicene Alexandrian Metonic lunar cycles have, as well as the archetypal Alexandrian lunar cycle, de facto limit dates 21 March and 18 April, but each of the sequences of Paschal dates generated by them according to the new Alexandrian Paschal rule has de facto limit dates 22 March and 25 April.
We conclude that Anatolius can be regarded as the great founder, and the ante Nicene Alexandrian computists who constructed the archetypal Alexandrian lunar cycle and their great post Nicene follower Annianus as the most important developers, of the efficient Alexandrian Metonic lunar cycle method for determining Julian or Alexandrian calendar dates of Paschal Sunday from which, thirteen centuries after Anatolius’ death, because of the second great calendar reform in AD 1582, turning point in the history of chronology, an astronomically more realistic (but also more complicated) method for determining Gregorian calendar dates of Easter would be developed. ×