Although the month and date of Jesus’ birth are unknown, the church in the early fourth century fixed the date as December 25. This corresponds to the date of the winter solstice on the Roman calendar. It is exactly nine months after Annunciation on March 25, also the date of the spring equinox. Most Christians celebrate on December 25 in the Gregorian calendar, which has been adopted almost universally in the civil calendars used in countries throughout the world.