The story of calendar starts with Ancient Roman emperor Julius Caesar. He made his Julian calendar which had 365 days separated in 12 months. The Julian calendar also included a leap year in every four years that synced with the solar seasons. Romans once faced confusion in 46 BC as the leap year continued for 15 months totaling 445 days. Fun Fact, that year is also known as the year of confusion. However, after 46 B.C. the calendar worked perfectly for centuries. It was again in mid-16th century when the seasons started 10 days earlier than the season welcoming holidays like spring equinox. To bring a solution to the dilemma, Pope Gregory XIII introduced the Gregorian calendar in 1582, which is the same as the Julian calendar but with the exclusion of leap years and addition of a single day to every fourth year. Gregory added that day to February as the month was left with fewest days. And that’s how we got the February 29th as Leap Day. Note that at some point, the Gregorian calendar may have to be re-evaluated as it slips out of sync with solar years. But it will take around thousand years for this to happen.