In 46 BCE Julius Caesar introduced more changes, though the Julian calendar, as it became known, retained January 1 as the year’s opening date. With the expansion of the Roman Empire, the use of the Julian calendar also spread. However, following the fall of Rome in the 5th century CE, many Christian countries altered the calendar so that it was more reflective of their religion, and March 25 (the Feast of the Annunciation) and December 25 (Christmas) became common New Year’s Days.