The Julian Calendar is a calendar system introduced by Julius Caesar in 45 BCE. It was designed to simplify the Roman calendar by establishing a year of 365 days, with an extra day added every four years, creating a leap year. This system aimed to align the calendar year with the solar year, which is approximately 365.25 days long. Despite its improvements, the Julian Calendar still miscalculated the solar year by about 11 minutes. This discrepancy led to a gradual drift of the calendar with respect to the seasons. Eventually, the Gregorian Calendar, introduced by Pope Gregory XIII in 1582, replaced the Julian Calendar to correct this drift.