Dionysius Exiguus, also known as , was a monk and, above all, a learned fifth-century Christian. He is best known for introducing the Anno Domini (AD) dating system, which is still used today.
Main contributions
Calculation of the Annus Domini: Dionysius calculated the year of Jesus' birth using historical and astronomical sources. He set the date at 25 December 753 after the founding of (AUC — ab urbe condita), corresponding to year 1 of the Christian era.
Translations and canon law: He translated many texts from Greek into Latin, including canons of church councils and theological treatises. His work helped harmonise Christian calendars and establish the date of Easter.
Collaboration with Pope John I: At Pope John I's request, Dionysius worked to establish a method of calculating dates that would end the Easter disputes and unify Christian calendars (year 625).
Calculation error: According to many historians, Dionysius Exiguus probably made a calculation error. Indeed, most historians support the hypothesis that Herod the Great died in 4 BC. We, however, favour the alternative hypothesis of a death in 2 BC, which would imply that Dionysius Exiguus was one year out in his references, which are not absolutely precise. We also acknowledge an inaccuracy concerning the day of the year. This, however, is not attributable to Dionysius Exiguus but dates back to the in 325. It is highly likely that Dionysius Exiguus knew that 25 December was not the day of Jesus' birth. In Israel, even at that time, shepherds were unlikely to remain outdoors with their flocks in winter (Luke 2.8-12). This situation reflects a complex interaction between politics and history. Indeed, Dionysius Exiguus did not challenge the date of 25 December, probably under pressure from the hierarchy. He thus undoubtedly, though unintentionally, endorsed this obvious error.
Impact and legacy
Dionysius Exiguus's work had a lasting impact on how we date historical events and helped standardise Christian festivals, notably the celebration of Christmas on 25 December.