Dionysius Exiguus and the AD Calendar System

When the AD calendar system was created, by whom, and for what purpose.

The beginnings of the AD calendar system can be credited to Dionysius Exiguus. He was a sixth-century Scythian monk who lived in what is now known as Romania.

Ironically, his intent was not to create a new time-system, rather, it was expressly designed to allow all Churches throughout Christendom to celebrate Easter on the same day. Churches celebrating Easter on different days existed for centuries and was considered a major problem during his time.

In Dionysius’ description of a new calendar, he provided a graphic table, much similar to an Excel spreadsheet, with different reference systems to calculate Easter. Dionysius main concern was to fix the Easter rite correct for every year because the previous table was almost complete. The lunar cycle was of the utmost importance for calculating Easter and had to be correlated with the Julian calendar. In order to accomplish this, he had a 7-point system. Two of the more important ones to dating the birth of Christ were the indictions and the then accepted 19-year lunar cycle. The indictions were a 15-year cyclical taxation system first initiated by Julius Caesar in 48 B.C.1

One of the intents of Dionysius’ dating system was to totally eliminate the name of the Emperor Diocletian in any reference to a time chart. The AD first meant “Anni Diocletiani” which related to the beginning of his reign at 284 AD. Diocletian’s laws, persecutions and punishments against the Christian community were severe. So great was his persecution that Dionysius did not believe it was right to associate the acronym AD with his name and changed it. The following is found in his work, Liber de Paschate Praefatio.

Verily the holy Cyril began the first cycle from the 143rd year of Diocletian and ended in the 247th year, rather than commence by the leader in the 248th year from the Tyrant, we did not wish to include in our circle the memory of an impious and persecutor, but we chose above to mark the time from the year of the incarnation of our Lord Jesus Christ.2

The table devised by Dionysius began at 513 AD which was 229 years after the start reign of Diocletian. He marked the first 229 years as “Anno Diocletiani.” Then at 532 AD he changed the acronym to mean “Anni Domini nostri Jesu Christi.” His table ends at 626 AD with no reference to the reign of Diocletian.

It is not an easy read, as the variables he used are not contemporary ones.

The best place to start reading and understanding the Dionysius English text from especially a mathematical perspective is Michael Decker’s article, Nineteen Year Cycle of Dionysius. It is not the prettiest web page but full of important information.

For more information

  1. See Liber De Pascate Sive Cyclus Paschalis. MPL 67, as found at Documenta Catholica Omnia, Col. 494Ff
  2. Liber de Pashcate Praefatio. My personal translation into English

3 thoughts on “Dionysius Exiguus and the AD Calendar System”

  1. is it better to try to ascertain the date for the birth of christ and celebrate it
    as a religious holiday or should we be satisfied with the fact that he was born of the virgin mary in bethlem in the last year of herod,s reighn?

    • If I understand your question correctly, you are asking about the importance of Christ’s birth — is it a religious rite to be held once a year that can be traced through history, or is it the nature and purpose of the birth we are celebrating? Of course the nature and purpose is more important. Although the meaning has been clearly established, the actual historical details related to dating the birth year have rarely been critically looked at. This was the purpose of the article.


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