The Roman calendar:

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, which lasted 365.25 days.

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

Here you have more information (in Spanish) about its origins, evolution and characteristics: