What Is the Meaning of AD?

Pretty much everyone knows that B.C. means "Before Christ," but what does A.D. stand for? How did we get the A.D. system in the first place?

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Updated Nov 08, 2023
What Is the Meaning of AD?

What Is the Meaning of AD?

Most of us know what B.C. stands for, but what does A.D. stand for? Here’s what you need to know about this term and how it became the accepted way to  

What Does AD Stand for?

AD stands for Anno Domini. Anno is Latin for “in the year,” domini is Latin for “lord,” so Anno Domini translates as “in the year of our Lord.” Since Christianity maintains that Jesus is still living—ascended to heaven, at the father’s right hand—every year since his birth is a year of our Lord.

A.D. lists all the years since Christ’s birth, while the years before his birth are listed as B.C., “Before Christ.” The dating system goes from 1 B.C. to 1 A.D.—contrary to popular belief, there is 0 A.D. Following this dating system, Jesus (at least in theory) was born in the year 1 A.D. Whether he was actually born in what we know as 1 A.D. depends on whether the person who calculated the dating system got the year exactly right (something that will be discussed later).

When Did People Start Using the AD System?

Like most innovations, the A.D. dating system has several precedents, and it’s difficult to say who invented the first version. However,  we can establish who popularized the version we use today.

The A.D. system we use was developed by a monk named Dionysius Exiguus. Exiguus developed his dating system to deal with a problem Christians faced figuring out when to celebrate Easter. As explained in the article, “How Old Was Jesus When He Died and How Do We Know?” Exiguus lived in a period where many Christians used an Easter timetable built on anno Diocletian, the period when the Roman emperor Diocletian reigned. Diocletian’s period was also called “the era of the martyrs” because Diocletian increased the persecution of Christians, killing more of them than previous Roman emperors. Exiguus didn’t feel it was proper to determine when to celebrate Easter using a system named after such a bloody emperor, so he devoted his time to creating a new system. Exiguus claimed the year he made his dating system was 525 years since Jesus’ incarnation.

After Exiguus proposed the system, it took a while to catch on. Over a century later, in 672 or 673 A.D., a man named Bede (often known today as the Venerable Bede) was born. Bede became a monk who wrote prolifically, mostly history. Two of his books, The Reckoning of Time and The Ecclesiastical History of the English People, used the A.D. system or a close variant and helped popularize its use. Charlemagne made A.D. more popular as ruler of the Carolingian empire, and by the end of the 800s, many European counties were using it. Most European countries began using it officially in their calendars between the 14th and 16th centuries. Many Eastern countries, particularly those following Eastern Orthodoxy with its Byzantine calendar, didn’t use the A.D. system until 1700 when Russian tsar Peter the Great announced changes in the Russian calendar.

About a century before Peter the Great made A.D. standard for Russia, the term B.C., “Before Christ,” became popular. Bede and others used similar terms—Bede used a Latin phrase that translates as “before the incarnation of our Lord.” In 1627, French theologian Denis Pétau used the phrase ante Christum in his book Opus de doctrina temporum, and later scholars working from Latin to English developed the English version, “Before Christ.”

What Did People Use Before the BC/AD System?

Before the B.C./A.D. system was developed, different cultures had various ways of stating the year they lived in. Many of these cultures used regnal years—the current year of the reigning king. Ancient Egyptian historians might state “year 1 of Cleopatra VII.” The regnal year system had a vital impact on the A.D. system for a simple reason: there can’t be a year zero of a king’s reign. The year that a king becomes a king is year 1 of his reign. Dionysus Exiguus followed this concept for his A.D. system, and thus there is no 0 A.D.

Even as European countries accepted the A.D. and B.C. dating systems, there were smaller issues related to the ones that Exiguus had tried to solve. As the article “What Is Greek Easter and How is it Different?” explains, the Roman empire adopted the Julian calendar in 45 BC. The Western hemisphere replaced it with the Gregorian calendar during the late 16th century. Eastern Orthodox churches didn’t apply the Gregorian calendar to their religious feasts, which is why most Eastern Orthodox Christians celebrate Easter on a different date than the rest of the Western hemisphere. So, the problem that prompted Exiguus to create a new dating system (coming up with a new, better way for everyone to calculate the date to celebrate Easter) has continued to plague different denominations in new ways.

Is the BC/AD System Accurate?

Whether or not Exiguus got his math right when he said it was 525 years since Christ’s birth is up for debate. Scholars have argued back and forth about why he picked that precise number. Some have speculated he picked a number over 500 because many Christians of his time speculated Jesus’ second coming would be 500 years after his birth. Saying it had been over 500 years would have allowed Exiguus to squelch that particular End Times theory or avoid panic from people thinking they had only a handful of years before Jesus came back.

Interestingly, scholars agree that Exiguus wasn’t wildly off. Based on the New Testament’s references to when Jesus was born (when Herod the Great ruled Judea, born during a census by Caesar Augustas, at a time when Quirinius governed Syria), Exiguus appears to have missed his mark by four to six years. So, Jesus was actually born sometime around 4 B.C.

You may feel discouraged that we’ve misstated Jesus’ birth date for so long. However, the fact that calculations were less than a decade off is impressive, considering that Exiguus made his calculations over five centuries after Jesus was born. His proximity to the correct date is also impressive when you consider that historians don’t know the birth dates of many ancient historical figures. Studying ancient history often requires working with documents summarizing events centuries after the fact. Sometimes these documents give clear references that scholars can cross-reference with other accounts to establish the date; sometimes, the documents don’t give any clear references. Even with well-known figures like Diocletian, one of the most notorious Roman emperors, birth dates are not always certain. At present, scholars know when Diocletian became emperor and when he died, but not precisely when he was born. His birth occurred sometime between 242 A.D. and 245 A.D., during December, in a province called Dalmatia. Scholars have presented various arguments for which of those three years he was born, but it’s hard to be definite.

The fact that we’ve miscounted Jesus’ birth date doesn’t mean we know nothing about him or that we can’t affirm he existed. Lawrence Mykytiuk observes in an article for Biblical Archeology Review, “As far as we know, no ancient person ever seriously argued that Jesus did not exist.” Mykytiuk also explains that few contemporary scholars argue that Jesus didn’t exist. The evidence for his historical existence is very solid by any standard.

Further Reading:

How Old Was Mary When She Had Jesus?

How Old Was Mary When Jesus Died?

How Old Is God According to the Bible?

Photo Credit: Mosaic of Jesus Christ found in the old church of Hagia Sophia in Istanbul, Turkey ©iStock/Getty Images Plus/nodostudio

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