The Julian calendar

To start his new calendar, Julius Caesar stretched one year far beyond its usual length. By Censorinus's count, 46 BCE lasted 445 days; Macrobius made it 443, and called it the last year of confusion.

The Roman year before Caesar had 355 days. To keep it in step with the seasons, the pontiffs (the priests in charge of the calendar) inserted an extra month of 22 or 23 days in February, in alternate years. Some pontiffs stretched or shortened a year for political reasons. By Caesar's time, the biographer Suetonius wrote, the harvest festivals no longer fell in summer, nor the festivals of the grape harvest in autumn. As chief pontiff, helped by the scholar Sosigenes, Caesar added ten days to the months, making a year of 365 days, and ruled that one extra day be inserted every fourth year. It went in late February, by counting the sixth day before the Kalends (the first day) of March twice. From this comes "bissextile," "twice sixth," an old name for a leap year. The new calendar began on January 1, 45 BCE.

The reform soon went wrong. The priests inserted the extra day every third year, not every fourth. In 36 years, Macrobius says, they added twelve days instead of nine, until Augustus ordered twelve years with no leap day. Quintilis was renamed July, for Caesar, in 44 BCE, and Sextilis became August, for Augustus, a change Smith's Dictionary dates to 8 BCE.

A Julian year of 365¼ days is a little longer than the year of the seasons, which lasts 365 days and nearly 5 hours and 49 minutes. The church worked out Easter from the spring equinox, which it reckoned as March 21, a rule later credited to the Council of Nicaea in 325. By the 1580s the calendar had slipped ten days behind the sun. Pope Gregory XIII reformed it in 1582, but England kept Caesar's calendar until 1752.

In the library, How the Romans fixed the year, by Censorinus (238 CE), gives the most exact surviving account of the reform. Where the months got their names, by Macrobius, tells how the priests misread Caesar's rule and copies out the senate's decree renaming Sextilis for Augustus. What to do on the farm each month and A diary for every day of the year were written in England while it still kept the Julian calendar.