Anno Domini (Latin: "In the year of the Lord"), or more completely Anno Domini Nostri Jesu Christi ("in the year of our Lord Jesus Christ"), commonly abbreviated AD or A.D., is the designation used to number years in the dominant Christian Era in the world today. This is the conventional designation now used with the Julian and Gregorian calendars. It defines an epoch based on the traditionally reckoned year of the birth of Jesus. Years before the epoch were denoted a.C.n. (for Ante Christum Natum, Latin for "before the birth of Christ"), although BC (Before Christ) is now usually used in English. The Christian Era is the only system in everyday use in the Western World, and the main system for commercial and scientific use in the rest of the world. However, in academic historical and archaeological circles, the same epoch is often referred to as the Common Era (CE) and the BC period as Before the Common Era (BCE).
While it is increasingly common to place AD after a date, by analogy to the use of BC, formal English usage adheres to the traditional practice of placing the abbreviation before the year, as in Latin (e.g., 100 BC, but AD 100).
History of dating in the Christian world
Anno Domini dating was not the initial choice of Christians in the Mediterranean world; actually, it was not adopted in Western Europe until after the end of the Western Roman Empire. Like the other inhabitants of the Roman Empire, early Christians used one of several methods to indicate a specific year — and it was not uncommon for more than one to be used in the same document. This redundancy, in fact, allows historians to construct parallel regnal lists for many kingdoms and polities by comparing chronicles from different regions which include the same rulers.
The earliest and most common practice was consular dating. This involved naming both consulares ordinares who had been appointed to this office on January 1 of the civil year. Sometimes one or both consuls might not be appointed until November or December of the previous year, and news of the appointment may not reach parts of the empire for several months into the current year; thus we find the occasional inscription where the year is defined as "after the consulate" of a pair of consuls.
Dating from the founding of Rome
One common method of dating — which was not as common as thought by moderns — was to indicate the year ab urbe condita, or "from the foundation of the City" (abbreviated AUC), where "the City" meant Rome. This style was not in common use because of long standing disagreements over the exact year Rome was founded. However, with the Millennial Games celebrated by the emperor Philip, the year 753 BC came to be widely accepted. This style became more common in order to reinforce the ideology of the Eternal City in times when the political order appeared insecure.
Regnal years of Roman emperors
Another system that is less commonly found than thought was to use the regnal year of the Roman emperor. At first, Augustus would indicate the year of his rule by counting how many times he had held the office of consul, and how many times the Roman Senate had granted him Tribunican powers, carefully observing the fiction that his powers came from these offices granted to him, rather than from his own person or the many legions under his control. His successors followed his practice until the memory of the Roman Republic faded (late in the 2nd century or early in the 3rd century), when they openly began to use their regnal year.
Another common system was to use the indiction cycle (15 indictions made up an agricultural tax cycle, an indiction being a year in duration). Documents and events begin to be dated by the year of the cycle (e.g., "fifth indiction", "tenth indiction") in the 4th century, and was used long after the tax was no longer collected. This system was used in Gaul, in Egypt until the Islamic conquest, and in the Eastern Roman Empire until its conquest in 1453.
Other dating systems
A great many local systems or eras were also important, for example the year from the foundation of one particular city, the regnal year of the neighboring Persian emperor, and eventually even the year of the reigning Caliph. The beginning of the notational year also varied from place to place, and was not largely standardized in Europe (except England) as January 1 until the 16th century. The most important of these include the Seleucid era (in use until the 8th century), and the Spanish era (in use in official documents in Aragon, Valencia, and in Castile, into the 14th century, and reportedly even later in Portugal).
After the Roman Empire
As the Roman Empire declined, imperial regnal year dating became sloppy, but remained the norm for 400 years in Christian Church circles. Use of consular dating ended when the emperor Justinian discontinued appointing consuls in the mid-6th century. The last consul nominated was Anicius Faustus Albinus Basilius in 541. The Papacy was in regular contact throughout the Middle Ages with envoys of the Byzantine world, and had a clear idea — sudden deaths and deposals notwithstanding — of who was the Byzantine emperor at any one time.
The Anno Domini system was developed by a monk named Dionysius Exiguus (a Scythian) in Rome in 525, as an outcome of his work on calculating the date of Easter. Byzantine chroniclers like Theophanes continued to date each year in their world chronicles on a different and much more popular Judaeo-Christian basis — from the notional Creation of the World as calculated by Christian scholars in the first five centuries of the Christian era. These eras, sometimes called Anno Mundi , "year of the world" (abbreviated AM), by modern scholars, had their own disagreements. The most popular formulation was that established by Eusebius of Caesarea, a historian at the time of Constantine I. The Latin translator Jerome had made a comparison of Eusebius with certain dates deduced from the Old Testament which helped popularize Eusebius's AM count in the West.
Accuracy of dating
Almost all Biblical scholars believe that Dionysius was incorrect in his calculation, and that Jesus Christ was actually born between 8 BC and 4 BC. The latest bound for the birth of Christ is the death of Herod the Great which occurred in 4 BC. This is not a very controversial point, as no Christian denomination's theology requires the date to be 1 BC, and some minority beliefs do not accept that date at all.
The popularization of Anno Domini
The first historian or chronicler to use Anno Domini as his primary dating mechanism was Victor of Tonnenna , an African chronicler of the 7th century. A few generations later, the Anglo-Saxon monk Bede, who was familiar with the work of Dionysius, also used Anno Domini dating in his Ecclesiastical History of the English People, finished in 731. Bede was different from historians working in more important places in two ways: First, he was in Northumbria, outside the bounds of the later Roman Empire. Unlike the Mediterranean-focused countries of Italy, France, and Spain, his people had little knowledge of or interest in who the Roman Emperor was in any particular year. Second, he was confronted with the problem of seven Anglo-Saxon kingdoms and their overlapping regnal years. He had also previously written a chronicle going back to Creation, so he had the numbers at his fingertips. He adopted Anno Domini dating as a way of keeping track of the Anglo-Saxon kingdoms and trying to bring their dates into line with the fragmentary evidence he had for imperial regnal years. In this same history, he was the first to use BC and established the standard for historians of no year zero, even though he used zero in his computus.
On the continent of Europe, Anno Domini was first used as the dominant dating system by Charlemagne and his successors, having learned of it through the Northumbrian scholar Alcuin. It was this influence of the Royal Frankish court that popularized the usage and spread it east into German speaking territories. The Carolingian use of AD may well have had twin ideological reasons of breaking away from using the Byzantine era and defusing certain strains of apocalyptic thought.
Two lesser known systems competed for a while with the Anno Domini system. The earliest was the Era of Martyrs , which numbered years from the accession of Diocletian in 284, who launched the last yet most severe persecution of Christians. This system is still used officially by the Coptic and Ethiopian churches. The other system was to date from the Death of Jesus Christ, which as early as Hippolytus and Tertullian was believed to have occurred in the consulate of the Gemini (AD 29), which appears in the occasional medieval manuscript.
Alternative methods in the modern era
The French Revolution and the Italian Fascists each seriously attempted to displace the Anno Domini system by instead dating from their own foundings — a non-royal regnal year system (see French Revolutionary Calendar). The Italian Fascists actually used the standard system along with Roman numerals denoting the number of years since the establishment of the Fascist government in 1922. Therefore, 1934, for example, was Year XII. Both attempts ultimately failed to replace the standard calendar. North Korea uses a system that starts in 1911, the year before the birth of their founder Kim Il-Sung, the year 2004 is "Juche 93" in this system because it is the 92nd year after the Juche leader's birth.
In the Islamic world, traditional Islamic dating according to the Anno Hegirę (in the year of the hijra) era remains in use to a varying extent, especially for religious purposes. In Israel, the traditional Hebrew calendar, using an era dating from Creation, is in official use.
- Declercq, Georges. Anno Domini: The origins of the Christian era. Turnhout: Brepols, 2000. ISBN 2503510507 (despite beginning with 2, it is English)
- ———. "Dionysius Exiguus and the Introduction of the Christian Era". Sacris Erudiri 41 (2002): 165–246. An annotated version of part of Anno Domini.
- Richards, E. G. Mapping Time. Oxford: Oxford University Press, 2000. ISBN 0192862057
- The Catholic Encyclopedia, s.v. "General Chronology"
- The Catholic Encyclopedia, s.v. "Christian Era"