Ante Christum Natum usually abbreviated to A.C.N., a.C.n., a.Ch.n. or ACN, denotes the years before the birth of Jesus Christ. It is the modern Latin equivalent to the English term "BC" ("Before Christ") and "BCE" ("Before Common Era"). The phrase Ante Christum Natum is also seen as the shorter Ante Christum (Latin for "Before Christ"), again usually abbreviated to A.C. or AC. A related term, p.Ch.n or post Christum natum complements a.Ch.n and is equivalent to "AD".

These terms are chiefly found in modern Latin texts. English speakers are unlikely to recognize them. Neither the Chicago Manual of Style (14th ed.), the American Heritage Dictionary (3rd ed.), nor P. Kenneth Seidelmann's Explanatory Supplement to the Astronomical Almanac (1992, University Science Books) mention AC, ACN, or Ante Christum Natum.

These terms were not used in medieval

Middle Ages

The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

 and Renaissance

Renaissance

The Renaissance was a cultural movement that spanned roughly the 14th to the 17th century, beginning in Italy in the Late Middle Ages and later spreading to the rest of Europe. The term is also used more loosely to refer to the historical era, but since the changes of the Renaissance were not...

 Latin texts. Bede the Venerable

Bede

Bede , also referred to as Saint Bede or the Venerable Bede , was a monk at the Northumbrian monastery of Saint Peter at Monkwearmouth, today part of Sunderland, England, and of its companion monastery, Saint Paul's, in modern Jarrow , both in the Kingdom of Northumbria...

, who was the first writer to identify a year as before Christ, used the Latin ante incarnationis dominicae tempus (before the time of the Incarnation of the Lord) in his Historia ecclesiastica gentis Anglorum

Historia ecclesiastica gentis Anglorum

The Historia ecclesiastica gentis Anglorum is a work in Latin by Bede on the history of the Christian Churches in England, and of England generally; its main focus is on the conflict between Roman and Celtic Christianity.It is considered to be one of the most important original references on...

(I.2) in 731. Most comparable early Latin terms referred to Christ's Incarnation

Incarnation (Christianity)

The Incarnation in traditional Christianity is the belief that Jesus Christ the second person of the Trinity, also known as God the Son or the Logos , "became flesh" by being conceived in the womb of a woman, the Virgin Mary, also known as the Theotokos .The Incarnation is a fundamental theological...

or conception, not his birth nine months later.