The author of this study was born in 1938, studied mathematics, physics, and astronomy at the university of Utrecht from 1960 to 1969, and was a teacher of mathematics from 1970 to 2001 at the Gymnasium Celeanum in Zwolle. After having steeped oneself in the fields of history of mathematics, history, and chronology, he became fascinated by the computus paschalis, i.e. the science developed since the beginning of the third century on behalf of the determination of the date of Easter Sunday. In 2009 he succeeded in determining the initial year AD 271 of De ratione paschali, i.e. the medieval Latin text containing the Paschal tract of the famous third century Alexandrian computist Anatolius. He did it by reconstructing the proto-Alexandrian 19-year lunar cycle defined to be the Metonic 19-year lunar cycle necessarily used by Anatolius to construct his legendary 19-year Paschal cycle. The reconstruction in question was the subject of his contribution to the international conference on the science of computus which took place at the university of Galway in 2010. It was published in 2017 as an article in the proceedings of that conference under the title “The initial year of De ratione paschali and the relevance of its paschal dates”. In the meantime (from 2001 to 2018) he kept up a sextilingual website (named millennium) on chronology.
This new study developed from the presentation he gave at the university of Galway in June 2018 under the title “Reconstructing the Alexandrian 19-year lunar cycles”. Because the paper in question was accepted outside the theme of the conference, it should not be included as an article in the proceedings of the conference. Therefore the author, convinced of the relevance of his recent discoveries, decided, in view of his old age and in order to lose no time, to publish these new results on his own in the form of this book, however not without dedicating it to his great teacher and friend Professor Daniel P. Mc Carthy, who, always attentive, went on critically following the development of his ideas during the last ten years, and expressing his gratitude to his beloved wife Marie Luijters for her unconditional patience with his new ambition.