What concept did Ancient Rome create for timekeeping by adding a specific extra day in certain years?

The concept that Ancient Rome developed for timekeeping by incorporating an additional day in certain years is known as the leap year system. This system was designed to keep the calendar year synchronized with the astronomical year. Since a solar year is not exactly 365 days but approximately 365.24 days, the leap year system introduced an extra day every four years to correct the discrepancy. This adjustment ensures that our calendar remains aligned with the seasons over time, preventing significant shifts in the calendar.

While the term "bissextile year" also refers to the occurrence of an extra day in leap years, it is essentially a term used in conjunction with the leap year system rather than a concept created on its own. Solar and lunar timekeeping are different methods of measuring time based on the sun and moon cycles, respectively, but they do not specifically address the adjustment of the calendar through the addition of an extra day. The leap year system is a crucial aspect of how Ancient Rome structured their calendar to maintain temporal accuracy.