Ever wondered why we start the new year (and why so many people consequently begin it with a horrific hangover) on Jan. 1? You can thank the most famous Roman emperor of all. It all started on this day in 45 B.C.

Julius Caesar looked at his calendar and growled. If modern slang had existed in ancient Rome, he would have called it a “hot mess.” Because that’s just what the Roman calendar of his day was, and it caused lots of problems.