It was 46 BC. Julius Caesar stretched that year out to a whopping size. He wanted to make the following year begin at the right time again: that is, after the winter solstice.
Using the best astronomy and mathematics of the time, Caesar tinkered the old Roman calendar to make it fit the reality of the solar year. That’s the year of 365 days (plus a few hours) that we take for granted today. We still divide it into 12 months, and still call them by their Roman names. But to begin this new measure of time, Caesar declared a transitional year of 445 days.