Ab urbe condita

‘Ab urbe condita’ AUC means ‘from the founding of the City’ (of Rome) on the 21st April 753 BCE.
1 AUC is 753 BCE

In 753 BCE 21st April, the Romans believed the City of Rome was founded on the Palatine Hill by Romulus.
In 121 CE, the 21st April became the new festival of ‘Roma Aeterna’, the Goddess of the City of Rome. The ‘Dies Natalis Urbis’ meant ‘birthday of the city’. The festival included chariot races.
In 248 CE Rome celebrated its first millennium, 1,000 AUC, under Philip the Arab.

Palatine Hill, Rome