Fragment

Sumary
The development the Alexandrian method for determining Alexandrian or Julian calendar dates of Paschal Sunday underwent is nothing less than the mainstream of the history of 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) the solid construction (on the basis of at the time relatively recent lunar tables) of the proto Alexandrian lunar cycle (around AD 260) and Anatolius’ lunar cycle (around AD 270), the former being the (lost) Metonic lunar cycle from which the great third century Alexandrian computist Anatolius originally started to determine his Paschal dates, the latter being the one from which he ultimately started in order to construct his famous 19 year Paschal cycle;
2) the solid construction (idem) of the archetypal Alexandrian lunar cycle (around AD 320), being the (lost) Metonically structured common archetype of the three (well-known) post Nicene Alexandrian Metonic lunar cycles.
The proto Alexandrian lunar cycle and Anatolius’ lunar cycle were constructed in the third quarter of the third century, the archetypal Alexandrian lunar cycle was constructed already half a century later, shortly before the first council of Nicaea in AD 325, turning point in the history of Christianity. And so it must have been not so much because of different moments of construction as because of different sets of computistical principles according to which they were constructed that the latter lunar cycle differs so much from both the former ones. After having reconstructed them, we establish that:
1) there exists a 2 day gap (in fact a systematic difference of on average just over 2 days) 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 more familiar Egyptian lunar calendar instead of the Alexandrian version of the Jewish lunar calendar);
2) both the proto Alexandrian lunar cycle and Anatolius’ lunar cycle have de facto limit dates 23 March and 20 April, both sequences of Paschal dates generated by them have, according to the old Alexandrian Paschal rule, 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 each of the three (well-known) post Nicene Alexandrian Metonic lunar cycles would be obtained by accepting and whether or not adapting it by moving its saltus one or two years forward or afterward;
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, the four sequences of Paschal dates generated by them have, according to the new Alexandrian Paschal rule, de facto limit dates 22 March and 25 April.
We conclude that the Alexandrian computists who constructed the three lost ante Nicene Metonic lunar cycles, in particular the great scholar Anatolius (he died in about AD 282), can be regarded as the founders, their post Nicene followers Annianus (around AD 400), Dionysius Exiguus (around AD 500), and Bede (around AD 700) as the most important developers, of the efficient Alexandrian method for determining Julian calendar dates of Paschal Sunday from and thanks to which in the end, thirteen centuries after Anatolius’ death, an astronomically more realistic method for determining Gregorian calendar dates of Easter could be developed.
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