The BC / AD system was devised by a Christian monk named Dionysius Exiguus.
Who he was
- Dionysius Exiguus (“Dennis the Small”)
- A monk and scholar living in Rome in the early 6th century (around AD 525)
What he did
- He introduced the AD system — Anno Domini, Latin for “in the year of our Lord” — to number years based on what he believed was the year of Jesus Christ’s birth.
- His aim was practical, not historical: he wanted a better way to calculate Easter, and also to stop using a calendar era based on the reign of Emperor Diocletian, who had persecuted Christians.
What about BC?
- Dionysius did not invent “BC”.
- The idea of counting years before Christ (BC – “Before Christ”) was developed later and popularised in the 8th century by the English monk Bede (the Venerable Bede).
- Together, Bede’s work made BC/AD the standard system across Europe.
A small historical footnote
- Modern historians believe Dionysius probably miscalculated the birth year of Jesus by a few years, but the system stuck and became globally dominant.
1. Religious reference
- BC / AD explicitly refer to Jesus Christ
- AD = Anno Domini
- BCE / CE remove the religious wording
- CE = Common Era
📌 This makes BCE/CE more neutral for academic, international, or inter-faith use.
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