Ab urbe condita (AUC or a.u.c.) is Latin for "from the founding of the city" (of Rome), supposed to have happened in 753 BC. It was one of several methods used for dating years in the Roman era, when the Roman calendar and the Julian calendar were in use. It appears to have been widely replaced by the anno Diocletiani (A.D.) system instituted by Diocletian which in turn was gradually superseded by the anno Domini (A.D.) system of Dionysius Exiguus.
The traditional date for the founding of Rome of April 21, 753 BC was initiated by Varro. In practice the Romans typically dated events from the reign year of the current ruler (during the republic a consul had a term of a single year).
A new study claims that the Varronian date is superseded. Its correctness has not been proved scientifically but it is used worldwide. The foundation of Rome took place 437 years after the capture of Troy (1182 BC), according to Velleius Paterculus (VIII, 5). It took place shortly before an eclipse of the Sun that was observed at Rome on June 25, 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. Varro may have used the consular list with its mistakes, and called the year of the first consuls "245 ab urbe condita" (a.u.c.). He may have accepted the 244-year interval from Dionysius of Halicarnassus for the kings after the foundation of Rome. Some modern historians claim that an era "ab urbe condita" (from the founding of the city of Rome) did not, in reality, exist in the ancient world, and the use of reckoning the years in this way is modern.
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 June 15, 763 BCE, with a magnitude of 62.5% at Rome. Its beginning took place at 6:49, its middle at 7:47 and its end at 8:51.) He was born on the 21st day of the month Thoth. The first day of Thoth fell on March 2 in that year (Prof. E.J. Bickerman, 1980: 115). It means that Rhea Sylvia's pregnancy lasted for 281 days. Rome was founded on the ninth day of the month Pharmuthi, which was the 21st of 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 June 25, 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 turned into night, which sudden darkness was believed to be an eclipse of the Sun. It occurred on July 17, 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, on "Caprotine Nones," Livy (I, 21) also states that Romulus ruled for 37 years. He was slain by the senate or disappeared in the 38th year of his reign. Most of these have been recorded by Plutarch (Lives of Romulus, Numa Pompilius and Camillus), Florus (Book I, I), Cicero (The Republic VI, 22: Scipio's Dream), Dio (Dion) Cassius and Dionysius of Halicarnassus (L. 2). Dio in his Roman History (Book I) confirms our data by telling that Romulus was in his 18th year of age whan he had founded Rome. Therefore, three eclipse records prove that Romulus reigned from 746 BC to 709 BC, and Rome was founded in 745 BC.
Q. Fabius Pictor (c. 250 BC) tells that Roman consuls started for the first time 239 years after Rome's foundation (Enciclopedia Italiana, XIV, 1951: 173). Livy (I, 60) gives almost the same, 240 years for that interval. Polybius, The Histories (III, 22. 1-2) tells that 28 years after the expulsion of the last Roman king (or, in the 28th year, we believe), Xerxes crossed over to Greece, and that event is fixed to 478 BC by two solar eclipses. According to all these, The a.u.c. system should be handled accordingly, with due precaution.
Ab Urbe Condita is also the name of a work by Livy.
See also: List of Latin phrases