Thanks to William Shakespeare, Julius Caesar is forever linked with the calendar in the public mind. In the dramatization of Caesar’s life, a soothsayer warns him to “beware the ides of March” — the date on which Caesar was assassinated.

And today, we’re linked to Caesar by the calendar itself. He’s responsible for the basic calendar system we use today.

Before Caesar’s reform, the Roman calendar was a complete mess. The months didn’t match the cycle of seasons. Extra weeks were sometimes added between months, but they didn’t solve the problem. By Caesar’s time, the calendar and the seasons were way out of sync.

So Caesar asked the astronomer Sisogenes to help reform the calendar. Sisogenes recommended adding 67 days to the year that’s known today as 46 B.C. That would bring it into alignment with the seasons. He then outlined a year whose 12 months added up to 365 days. An extra day was added every fourth February to stay in time with the seasons.

The calendar was tweaked a bit over the following few years, and a change in the leap year was made many centuries later. Even so, the modern calendar is pretty much the one outlined by Sisogenes.

The Romans had a different way of numbering the days of the month, though. The middle of the month was known as the “ides,” while the start of the month was the “kalends.” So today is the kalends of January — the first day of a new year in a calendar made possible by Julius Caesar.

Script by Damond Benningfield