# Roman year a reference to the ancient calendar devised and used by the Romans. Very early in their history, the Romans began basing their calendar on the idea that 12 lunar months make a year. Each lunar month (from new moon to new moon) is about 291/2 days, so the Roman year came to 354 days. But the true solar year (the time it takes the Earth to circle the sun) is just under 365V4 days. The Romans made up for the difference by adding an extra month every few years.