What calendar did Ancient Rome implement that included a leap year?

Ancient Rome used the Julian calendar, which was established by Julius Caesar in 45 BCE. This calendar represented a significant reform of the Roman calendar system. One of its most notable features was the introduction of a leap year every four years, which added an extra day to the month of February. The Julian calendar was designed to align the calendar year with the solar year, ensuring that the seasons remained consistent over time.

This leap year system was crucial for maintaining the accuracy of the calendar, as it accounted for the fact that a solar year is approximately 365.25 days long. As a result, the Julian calendar became the standard for many countries in the Western world until the Gregorian calendar was introduced much later in 1582 to further refine the system.