How do we number the years? Long ago, every land counted its own way: from the founding of a city, or from the year a king began to rule. About AD 525, a monk named Dionysius Exiguus worked out a count starting from the birth of Jesus. In time, much of the world came to use it.
Key idea
Years after the birth of Jesus are marked AD (from the Latin anno Domini, "in the year of the Lord") and counted forward: AD 1, AD 2, AD 3… Years before are marked BC ("before Christ") and counted backward: 3 BC, 2 BC, 1 BC. There is no year 0: 1 BC is followed right away by AD 1.
So with BC dates, a bigger number is longer ago. Rome was founded (in legend) in 753 BC, and the first Olympic Games were held in 776 BC, 23 years earlier.
| To find years between… | Do this | Example |
|---|---|---|
| two AD dates | subtract | AD 1066 to 1492: 1492 − 1066 = 426 years |
| two BC dates | subtract (bigger minus smaller) | 776 BC to 753 BC: 776 − 753 = 23 years |
| a BC date and an AD date | add, then take away 1 (no year 0) | 44 BC to AD 14: 44 + 14 − 1 = 57 years |
Worked example: How long apart?
Julius Caesar died in 44 BC. The emperor Augustus died in AD 14. How many years apart were they?
- One date is BC and one is AD, so add: 44 + 14 = 58.
- There is no year 0 between 1 BC and AD 1, so take away 1: 58 − 1 = 57.
Answer: 57 years.
A century is 100 years. The years 1801 to 1900 are the 19th century, because they finish the 19th group of a hundred years. We live in the 21st century: the 2000s.
Common mistake
Reading 500 BC as later than 300 BC because 500 is the bigger number. With BC dates, bigger means earlier.
You may also see BCE and CE ("before the Common Era" and "Common Era"). They use the same numbers; only the letters are different. This course writes BC and AD.
Try it at home
- Make a time line of your own life on a long strip of paper: one hand-width for each year.
- Mark the year you were born, when you learned to walk, your first day of school, and other big moments.
- Then make a family time line: add the years your parents and grandparents were born.
Going further. Explore the Timeline of the Ancient World, from the pyramids to the fall of Rome. Older students practice with dates and periods in Dates and Periods.