The Roman calendar changed its form several times between the founding of Rome and the fall of the Roman Empire. The common calendar widely used today is known as the Gregorian calendar and is a refinement of the Julian calendar where the average length of the year has been adjusted from 365.25 days to 365.2425 days (a 0.002% change).

From at least the period of Augustus on, calendars were often inscribed in stone and displayed publicly. Such calendars are called fasti.

Today the Roman calendar contains the seasons in which the Romans gods (deities) were worshiped, the events when certain rituals and sacrifices were given to the Roman gods, the pagan feasts of Rome like; Christmas, Easter, Saturnalia etc, are all preserved and observed accodring to the Gregorian calendar.