The traditional date for the founding of Rome, 21 April 753 BC, is due to Marcus Terentius Varro (1st century BC). 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From Emperor Claudius (ruled 41–54) onwards, Varro's calculation superseded other contemporary calculations.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 and 147/148 respectively.
In 248, 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.