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Ab urbe condita

"Ab urbe condita" (Classical orthography: ABVRBECONDITÁ; Latin pronunciation: [ab ˈʊrbɛ ˈkɔndɪtaː]; related to "anno urbis conditae"; A. U. C., AUC, a.u.c.; also "anno urbis", short 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. 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.

The traditional date for the founding of Rome of 21 April 753 BC, was initiated by 1st century BC scholar Marcus Terentius 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 confirmed but it is still used worldwide.

From Emperor Claudius (reigned 41–54 AD) onwards, Varro's calculation superseded other contemporary calculations.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.