This being February 29 — Leap Day — today is costing you an extra day's interest if you're repaying a debt. On the bright side, its earning you a tiny bit more on your bank deposits.

Whom do we have to thank — or curse — for this extra day every four years? Julius Caesar and his lover, Cleopatra.

In 48 B.C., Julius Caesar was in Alexandria, Egypt, absorbing the culture and science — and decadence — of Cleopatra's capital. There he learned from an old sage named Acoreus about Egypt's calendar, which had a leap year.

At the time, the Roman calendar did not. Like most ancient calendars, it was based on the phases of the moon, which in one cycle take about 29.5 days. But 12 months of 29.5 days doesn't equal the true length of the year as measured by the orbit of the Earth around the sun. It's off by 11 days, so anniversaries, holidays, and entire seasons to drift backward on lunar calendars.

The ancient Egyptians had realized this and created a calendar 365??-days long — with the fraction averaged in by adding an extra day every four years.

When Caesar returned to Rome, he created a 365-day calendar with a quadrennial leap year, adding the extra day in February.

A minor hassle for some, perhaps, but certainly better than the alternative faced by the Romans. Back in 45 B.C., for instance, their lunar calendar had drifted backward by 80 days — nearly three months. Spring had become winter, and autumn came in the summer months.

To correct, this Caesar decreed that 45 B.C. would be 445 days long. Think about the extra interest on 80 extra days! No wonder they called it "The Year of Confusion."

by David Ewing Duncan