During the Roman Republic, several dates were given for the founding of the city between 758 BC and 728 BC. Finally, under the Roman Empire, the date suggested by Marcus Terentius Varro, 753 BC, was agreed upon, but in the Fasti Capitolini the year given was 752. Although the proposed years varied, all versions agreed that the city was founded on April 21, the day of the festival sacred to Pales, goddess of shepherds; in her honour, Rome celebrated the Par ilia (or Palilia). (The Roman a.u.c. calendar, however, begins with Varro’s dating of 753 BC.)

– via Founding of Rome on Wikipedia.