Understanding the Christian Calendar
Introduction
Every day people write dates such as 2026, 1945, or 1066. Most people rarely think about what these numbers mean or where the system came from. Yet the calendar used across much of the world today is closely connected to the life of Jesus Christ.
The system that divides history into BC and AD is based on a Christian understanding of time. It attempts to place the birth of Jesus at the centre of world history. This article explains how this calendar system began and what the terms BC and AD actually mean.
The Meaning of BC
The abbreviation BC stands for “Before Christ.” It refers to the years before the birth of Jesus. For example:
- 500 BC means five hundred years before the birth of Christ.
- 100 BC means one hundred years before the birth of Christ.
The numbers count backwards toward the birth of Jesus. As time moves forward, the numbers decrease until they reach 1 BC.
The Meaning of AD
The abbreviation AD comes from the Latin phrase Anno Domini, which means “in the year of the Lord.” It refers to the years after the birth of Jesus Christ.
Unlike BC, the AD label is placed before the number. For example:
- AD 30
- AD 500
- AD 2026
These years count forward from the time associated with the birth of Jesus.
Today, many historians also use the neutral terms BCE (Before Common Era) and CE (Common Era). These terms use the same numbering system but avoid explicitly religious wording (Blackburn and Holford-Strevens, 1999).
Who Created the AD Calendar?
The BC/AD system was introduced in the sixth century by the monk Dionysius Exiguus.
Dionysius was working on calculating the correct dates for Easter. At the time, Christians often dated years according to the reign of Roman emperors. Dionysius preferred to measure time from the birth of Christ instead.
Around AD 525, he proposed a new system that counted years from the incarnation of Jesus. His calculations placed the birth of Jesus at what he called AD 1 (Blackburn and Holford-Strevens, 1999).
Over time, this method of dating spread throughout Europe and gradually became the dominant historical calendar.
The Global Adoption of the Calendar
The system became widely used after the English monk Bede adopted it in his historical writings. Bede used both BC and AD when describing world history, which helped standardise the system.
By the Middle Ages, the BC/AD dating method had spread across much of Europe. Later, through European exploration, colonisation, and global trade, this calendar became widely adopted around the world.
Today the same system forms the basis of the Gregorian calendar, which is used internationally for civil, scientific, and economic purposes (Richards, 2013).
A Calendar Centred on Jesus
The BC/AD system reflects a particular view of history: that the life of Jesus marks a central turning point in time. For this reason, the calendar divides history into two major periods:
- Before Christ (BC)
- Anno Domini (AD)
Even in modern secular societies, this structure continues to shape how years are counted.
However, as later parts of this series will show, historians today believe the birth of Jesus probably occurred a few years earlier than AD 1. This does not change the structure of the calendar, but it does raise interesting historical questions about the timeline of Jesus’ life.
Conclusion
The BC and AD system is more than a simple way of counting years. It represents a historical attempt to organise time around the birth of Jesus Christ. Created in the sixth century and widely adopted across the world, it remains one of the most influential chronological systems ever developed.
Yet the system also contains a historical puzzle. If the calendar begins with the birth of Jesus, why do many historians believe He was actually born several years earlier?
The next article in this series explores an important feature of the calendar that helps explain this issue: the missing year zero.
References
Blackburn, B. and Holford-Strevens, L., 1999. The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-Reckoning. Oxford: Oxford University Press.
Richards, E.G., 2013. Mapping Time: The Calendar and Its History. Oxford: Oxford University Press.