**This**** webpage belongs to www.alexandriancomputus.net,
which is a website promoting [Jan Zuidhoek
(2019) Reconstructing Metonic
19-year Lunar Cycles (on the basis of NASA’s Six Millennium Catalog of Phases of the Moon): Zwolle], and
shows section Summary of this pioneering book, which is available via this website.**

**Summary**

**It**** is the development the Alexandrian Metonic 19-year lunar cycle method underwent
which formed the mainstream of the history of the computus paschalis that had risen in third century Alexandria
(Egypt) to eventually flow into the modern method of determining the Gregorian calendar date of Easter Sunday. Between the construction of the very first Metonic 19‑year lunar cycle by
the Alexandrian computist Anatolius (between AD 250 and 270)
and the replacement of the Julian
calendar with the Gregorian calendar (in the year 1582) it was only once, namely
shortly before the first council of Nicaea (AD 325), that in Alexandria a completely new Metonic 19‑year lunar cycle was created, if not
by only simply
advancing the dates of Anatolius’
19‑year lunar cycle by 2 days, then by constructing
it directly or indirectly on
the basis of contemporary lunar
tables. After having reconstructed both of these lost ante‑Nicene Metonic 19-year
lunar cycles, we establish that:**

**1) the first of them
(indeed referred to as ‘Anatolius’ 19-year lunar cycle’) is nothing but the proto-Alexandrian 19-year
lunar cycle reconstructed in 2009;**

**2) the second of them (referred to as ‘the archetypal Alexandrian 19‑year lunar cycle’) is nothing but the archetype from which after AD 325 one after another
each of the three well‑known post-Nicene Alexandrian Metonic 19‑year
lunar cycles was obtained simply by moving only
1 of the 19 different dates of its immediate predecessor one day forward
or back (see Table 8)****;**

**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);**

**4) both Anatolius’
19-year lunar cycle and the
sequence of Paschal dates generated by it
according to the old Alexandrian Paschal rule have de facto lower limit date 23 March;**

**5) the archetypal Alexandrian 19-year lunar cycle has de facto
lower limit date 21 March
but the sequence of Paschal dates generated by it according
to the new Alexandrian Paschal rule has de facto
lower limit date 22 March
(the same applies to the well-known three post‑Nicene Alexandrian Metonic 19-year lunar cycles).**

**We conclude that
Anatolius may be considered to
be the founder of the efficient Alexandrian 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 develop
a modern, astronomically more correct, system for determining
the Gregorian calendar date
of Easter Sunday.**

**© Jan Zuidhoek 2019-2021**