According to History.com, in 45 B.C. New Year's Day was celebrated on January 1st for the first time with the newly devised Julian calendar. On becoming one of the world's well-known dictators, Julius Caesar ordered for a new calendar cycle to be reformed. Enlisting the help of an Alexandrian astronomer, Sosigenes, he advised Caesar to follow the solar calendar like the Egyptians did. So, in 46 B.C, Caesar added forty-six calendar days, which meant the following year January 1st was the first day of the year. By 44 B.C., when Caesar was assassinated, Mark Anthony changed some of the calendar names. Fun way to exercise your new power, Mark.