The Roman Catholic Pope Gregory XIII creates the self-named Gregorian calendar based on the earth’s rotation around the sun as 365 days or a full year.
The heads of the Church change January 1 as the New Year and temporarily replaces it with Christmas Day or the Feast of the Annunciation — days with more religious significance.
With the help of mathematicians and astronomers, Julius Caesar changes the calendar from pre-Julian to Julian by adding an additional day every four years as a way to balance out the lunar and solar calendars.
Along with signifying the vernal equinox as the start of a new year, the ancient Babylonian festival of Akitu, honors the sky god, Marduk’s victory over the dastardly sea goddess, Tiamat.