Ab urbe condita
Ab urbe condita (related to Anno Urbis Conditae: AUC or a.u.c. or a.u.) is a Latin phrase meaning "from the founding of the City (Rome)", traditionally dated to 753 BC. AUC is a year-numbering system used by some ancient Roman historians to identify particular Roman years. Renaissance editors sometimes added AUC to Roman manuscripts they published, giving the false impression that the Romans usually numbered their years using the AUC system. In fact, modern historians use AUC much more frequently than the Romans themselves did. The dominant method of identifying Roman years in Roman times was to name the two consuls who held office that year. The regnal year of the emperor was also used to identify years, especially in the Byzantine Empire after 537 when Justinian required its use. Examples of continuous numbering include counting by regnal year, principally found in the writings of German authors, for example Mommsen's History of Rome, and (most ubiquitously) in the Anno Domini year-numbering system.
From Emperor Claudius (reigned AD 41–54) onwards, Varro's calculation (see below) superseded other contemporary calculations. Celebrating the anniversary of the city became part of imperial propaganda. Claudius was the first to hold magnificent celebrations in honour of the city's anniversary, in 48 AD, 800 years after the founding of the city. Hadrian and Antoninus Pius held similar celebrations, in 121 AD and 147/148 AD respectively.
During 248 AD, Philip the Arab celebrated Rome's first millennium, together with Ludi saeculares for Rome's alleged tenth saeculum. Coins from his reign commemorate the celebrations. A coin by a contender for the imperial throne, Pacatianus, explicitly states "Year one thousand and first", which is an indication that the citizens of the Empire had a sense of the beginning of a new era, a Saeculum Novum.
When the Roman Empire turned Christian during the following century, this imagery came to be used in a more metaphysical sense, and removed legal impediments to the development and public use of the Anno Domini dating system, which came into general use during the reign of Charlemagne.
Calculation by Varro 
The traditional date for the founding of Rome of 21 April 753 BC, was initiated by Varro. Varro may have used the consular list with its mistakes, and called the year of the first consuls "245 ab urbe condita", accepting the 244-year interval from Dionysius of Halicarnassus for the kings after the foundation of Rome. The correctness of Varro's calculation has not been proven scientifically but is still used worldwide.
Relationship with Anno Domini 
The Anno Domini year numbering was developed by a monk named Dionysius Exiguus in Rome during 525, as a result of his work on calculating the date of Easter. In his Easter table the year 532 AD was equated with the regnal year 248 of Emperor Diocletian. The table counted the years starting from the presumed birth of Christ, rather than the accession of the emperor Diocletian on 20 November 284, or as stated by Dionysius: "sed magis elegimus ab incarnatione Domini nostri Jesu Christi annorum tempora praenotare..." It is assumed Dionysius Exiguus intended either 1 AD or 1 BC to be the year of Christ's birth (a "year zero" does not exist in this calendar). It was later calculated (from the historical record of the succession of Roman consuls) that the year 1 AD corresponds to the Roman year DCCLIV ab urbe condita, based on Varro's epoch. This however resulted in that year not corresponding with the lifetimes of historical figures reputed to be alive, or otherwise mentioned in connection with the Christian incarnation, e.g. Herod the Great or Quirinius.
- 1 ab urbe condita = 753 Before Christ
- 2 AUC = 752 BC
- 749 AUC = 5 BC
- 750 AUC = 4 BC (Death of Herod the Great)
- 753 AUC = 1 BC
- 754 AUC = 1 Anno Domini
- 755 AUC = 2 AD
- 759 AUC = 6 AD (Quirinius becomes governor of Syria)
- 2753 AUC = 2000 AD
- 2766 AUC = 2013 AD
Alternative calculations 
||This section may contain original research. (April 2012)|
According to Velleius Paterculus the foundation of Rome occurred 437 years after the capture of Troy by the Achaeans (1182 BC). It occurred soon before an eclipse of the Sun that was observed at Rome on 25 June 745 BC and had a magnitude of 50.3%. Its beginning occurred at 16:38, its middle at 17:28, and its end at 18:16.
However, according to Lucius Tarrutius of Firmum, Romulus and Remus were conceived in the womb on the 23rd day of the Egyptian month Choiac, at the time of a total eclipse of the Sun. (This eclipse occurred on 15 June 763 BC, with a magnitude of 62.5% at Rome. Its beginning occurred at 6:49, its middle at 7:47 and its end at 8:51.) They were born on the 21st day of the month Thoth. The first day of Thoth fell on 2 March in that year. Rome was founded on the ninth day of the month Pharmuthi, which was 21 April, as universally agreed. The Romans add that about the time Romulus started to build the city, an eclipse of the Sun was observed by Antimachus, the Teian poet, on the 30th day of the lunar month. This eclipse on 25 June 745 BC (see above) had a magnitude of 54.6% at Teos, Asia Minor. It started at 17:49; it was still eclipsed at sunset, at 19:20. Romulus vanished in the 54th year of his life, on the Nones of Quintilis (July), on a day when the Sun was darkened. The day became like night, which sudden darkness was believed to be an eclipse of the Sun. It occurred on 17 July 709 BC, with a magnitude of 93.7%, beginning at 5:04 and ending at 6:57. (All these eclipse data have been calculated by Prof. Aurél Ponori-Thewrewk, retired director of the Planetarium of Budapest.) Plutarch placed it in the 37th year from the foundation of Rome, on the fifth of our July, then called Quintilis, also states that Romulus ruled for 37 years. He was either slain by the senate or disappeared during the 38th year of his reign. Most of these data have been recorded by Plutarch, Florus, Cicero, Dio (Dion) Cassius and Dionysius of Halicarnassus (L. 2). Dio in his Roman History (Book I) confirms this data by telling that Romulus was in his 18th year of age when he had initiated Rome. Thus, three eclipse calculations may be evidence for the suggestion that Romulus reigned from 746 BC to 709 BC, and Rome was founded during 745 BC.
Q. Fabius Pictor (c. 250 BC) tells that Roman consuls started for the first time 239 years after Rome's foundation. Livy gives almost the same, 240 years for that interval. Polybius tells that 28 years after the expulsion of the last Persian king Xerxes crossed over to Greece, and that event is fixed to 478 BC by two solar eclipses.
See also 
Notes and references 
- Dio uses "a.u." in his Roman History
- Literally translated as "From the city having been founded".
- Liber de Paschate, Migne Patrologia Latina 67 page 481 note f
- Suetonius, Lives of the Caesars: Tiberius, 49
- (Prof. E.J. Bickerman, 1980: 115)
- Quintilis, on "Caprotine Nones," Livy (I, 21)
- (Lives of Romulus, Numa Pompilius and Camillus), Plutarch
- (Book I, I), Florus
- (The Republic VI, 22: Scipio's Dream), Cicero
- Enciclopedia Italiana, XIV, 1951: 173
- I, 60
- Polybius, The Histories (III, 22. 1–2)
- References: Theodor Mommsen, History of Rome (1854–1856)