Understanding historical chronology: Years, decades, centuries, and millennia

• For events that occurred before Jesus’ birth, type ‘BC’ (an abbreviation for ‘Before Christ’) after the number of the year.
• • For example: 48 BC.
• For events that happened after Jesus’ birth, type ‘AD’ (an abbreviation for the Latin phrase anno domini, which means “Year of our Lord”) before the number of the year.
• • For example: AD 120.

• BCE (Before Common Era) = BC

• • For example: 48 BC becomes 48 BCE

• CE (Common Era) = AD

• • For example: AD 120 becomes 120 CE

Watch a video explanation on the History Skills YouTube channel:

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• If there isn’t a ‘BC’ or ‘AD’ next to a date, it is probably AD

• Before the birth of Christ, the number of years counts down, but after that, the years count upwards

• There is no year ‘0’: the year 1 BC is followed immediately by AD 1

• ‘BP’ after a number stands for ‘Before the Present’

• ‘Circa’ means ‘around about’ and is a small ‘c.’ before the year. For example: c. 50 BC

Since human history has occurred over tens of thousands of years, historians have had to develop a system to help them talk about large sections of time easily.

As a result, names are given to groups of years. The groups and their names are as follows:

• Decade               = 10 years

• Century              = 100 years

• Millennium       = 1000 years

Watch a video explanation on the History Skills YouTube channel:

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Therefore, time can be split into centuries or millennia, as is demonstrated below:

To make sense of the past, it is divided into even larger blocks of time called ‘periods’.

Each of these ‘periods’ can be broken down further into smaller times called ‘ages’ and even into smaller times called ‘eras’.