Christian era

The Christian era, sometimes called the Era of the Incarnation, was first used by Dionysius Exiguus (literally, “Denis the Little,” a name he gave himself), a Scythian monk (some say an abbot) living in Rome in the 6th century. Abbreviation, ad, for “anno Domini,” year of the Lord, which appears before the numerals.

At that time, to determine the date of Easter the Church relied on a table prepared by Cyril of Alexander (376–444 ce), showing the date of Easter. This table used the Diocletian Era, numbering years from the year that the Roman emperor Diocletian came to power (284 ce).

Pope John I asked Dionysius to extend this table. In doing so, Dionysius felt it was wrong to date the festival from the accession of a persecutor of the faithful, and so decided to number the years in his table from the time of Christ's birth.¹ Dionysius submitted his table in 525 ce.

It is pretty universally acknowledged that Dionysius did not manage to select the right year for Christ's birth, which was probably in 4 or 5 bce.

Dionysius' table fixed the date of the beginning of the Christian era that we still use, but it did not immediately lead to general use of the era–in fact, the oldest surviving historical work in which dates are given using the Christian era is the Ecclesiastical History of the English Nation, written early in the 8th century by the Venerable Bede (672?–735), a learned English priest.

English missionaries carried the use of the Christian era to the Franks (in present day France), where the court adopted it for certain purposes by the end of the 9th century.² From there it reached Italy, and was first used by the Papacy under John XIII (elected 965 ce). By the 11th century it was familiar in most of Europe, but not until the 14th century was it common in Spain. Greek-speaking Europe did not adopt it until the 15th century, and Russia not until 29 December 1699.

Its use in non-Christian countries only occurred with the adoption of the Gregorian calendar. Today it is frequently styled ce (for common era), but is numerically the same.

Bede also used bc (before Christ), but that didn't come into general use until the end of the 17th century.

1. G. Teres.
Time computations and Dionysius Exiguus.
Journal for the History of Astronomy, volume 15, pages 177-188 (1984).

2. R. L. Poole.
Imperial influences on the forms of Papal documents.
In Studies in Chronology and History.
Oxford: Clarendon Press, 1934.

Page 178.