Year notations are widely used for the Gregorian calendar (and its predecessor, the Julian calendar), for calendar eras, by almost all archaeology books and articles authors.

AD, ad, CE

‘AD’ means Anno Domini. This is the Christian era in the Gregorian calendar, starting from 1 AD as the year in which Christ was believed to have been born. (The date was calculated about 500 years after the event, so was a broad estimate.) If in lower case letters are used, this often means that the date is based on an uncalibrated radiocarbon date.

‘CE’ means Common Era, or Current Era. It is equivalent to ‘AD’ as a date and places the ‘common’ or ‘current’ era as being from the suggested birth of Christ at 1 AD, but, it removes the explicit claim of Anno Domini which means ‘year of our Lord’. First used almost 400 years ago, it has become especially popular from the late twentieth century to emphasize secularism or sensitivity to non-Christians.

BC, bc, BCE

‘BC’ means ‘Before Christ’. This signifies the pre-Christian era in the Gregorian calendar. This runs backwards from 1 BC. As with ‘bc’, the lowercase ‘bc’ often means that the date used is an uncalibrated date.

‘BCE’ means Before Common / Current Era. As with ‘CE’, it removes the explicit reference to Christ, but is still equivalent to ‘BC’ in date.

BP and bp

The initials ‘BP’ stand for ‘years before present’. The use of BP by archaeologists, geologists, and other scientists, refers to radiocarbon ages and results from other radiometric dating techniques. Radiometric dating techniques are those that provide absolute dates based on the decay of radioactive isotopes.

However, not everyone follows the use of upper case and lower case protocols.

For word order the ‘AD’ usually comes before the year number, as that is the correct order in Latin – so it is AD 1066. But, as ‘BC’ is English, it comes after the year number, so it is 3000 BC. Also, as ‘CE” is English, the abbreviation is written after the year numbers; so, AD 1066 is equivalent to 1066 CE. The abbreviation is also commonly used after the number of a century or millennium, as in ‘tenth century AD’ or ‘first millennium AD’.

Pre and Post

Although ‘Pre’ (before) and ‘Post’ (after) are widely used in modern algorithm notations, the new ‘BC and ‘AC’ seem to be gaining grounds in internet slang and abbreviations, assuring a new COVID era calendrical protocol…

Food for thought!