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Summary

It is the development of the Metonic 19-year lunar cycle that formed the mainstream of the history of the computus paschalis which had risen in third century Alexandria (Egypt) and would in the year 1582 flow into the modern method which since then is used in order to determine the Gregorian calendar date of Easter Sunday. Between the active construction of the first version of this lunar cycle by the Alexandrian computist Anatolius, somewhere between AD 250 and 270, and the replacement of the Julian calendar with the Gregorian calendar (in the year 1582) it happened only one time, somewhere between AD 300 and 324, in any case still before the first council of Nicaea, that a radically new version of this lunar cycle was actively constructed. After having reconstructed (on the basis of NASA’s Six Millennium Catalog) both these ante-Nicene versions of the Metonic 19-year lunar cycle, we establish that:

1) the first of them (referred to as ‘Anatolius’ 19-year lunar cycle’) is nothing but the lost proto-Alexandrian 19-year lunar cycle (reconstructed ten years ago);

2) the second (referred to as ‘the archetypal 19-year lunar cycle’) is nothing but the lost archetype from which after AD 325 one after another each of the three well-known post-Nicene Metonic 19‑year lunar cycles was obtained simply by moving only 1 of the 19 different dates of its predecessor one day forward or back;

3) the cause of the 2-day gap between them (referred to as ‘the ante-Nicene Alexandrian 2-day gap’) must be sought in the transition 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 began to use the Egyptian lunar calendar more familiar to them instead of the Alexandrian version of the Jewish lunar calendar.

We conclude that Anatolius was the founder of the efficient Metonic 19-year lunar cycle method of determining the Julian calendar date of Paschal Sunday from which thirteen centuries later the Italian astronomer Luigi Lilio and subsequently the German mathematician Christoph Clavius could depart to develop a modern, astronomically correct, system for determining the Gregorian calendar date of Easter.