Answer: only during Leap Year…
The great-grand-daddy of our February 29th Leap Day goes back to the ancient Romans. I know what you’re thinking: Don’t we have anything that doesn’t go back to them? Uh, yes: numbers, and thank god for that, or taxes would be an even bigger drag. Also the dates of the month aren’t Roman—for which you’ll be grateful in a minute.
See, back in the day, when the Romans used a lunar calendar, the full moon fell directly in the middle of each month and was called the Ides. And the new moon at the beginning of the month was called the Kalends (from which we get the word calendar). And somewhere in between those two were the Nones. (From which we get the word nine. The nones were nine days before the Ides.)
Instead of saying it’s March 13th, the Romans would say It’s two days before the Ides of March. (Actually they’d say it’s three days before the Ides because they counted funny and that’s another reason you should be glad for Arabic numbers, but that’s neither here nor there.) Instead of saying it’s March 25th, they’d say it’s six days before the Kalends of April, or ante diem IV Kalends Aprilis.
March marked the beginning of the new year. To make up for the fact that the lunar calendar was only 355 days long, every few years a mensis intercalaris, or intercalary month, was tacked onto the end of February. February 23 was the annual Terminalia holiday, in which Romans celebrated Terminus—no, not the god of airports—the god of boundary stones and property disputes. Kind of like the ancient Judge Judy.
Whether a year would have a mensis intercalaris tacked on was determined by the Pontifex Maximus. The problem with this system is if Ponty’s friends were in office, he would have reason to extend the calendar year, whereas if an opposing party had power, he would have reason to shorten it. As a result of this friction and the chaos of the Punic Wars, the intercalary months were added or forgotten for decades at a time. Soon the calendar drifted into entirely different seasons.
Julius Caesar formalized the calendar. Each month was lengthened a certain number of days so the whole calendar would mirror the solar year, not the cycles of the moon—365 days. Instead of a whole month, a leap day was inserted after February 23 (or February 24) every four years.
Only they didn’t call it the 23rd or 24th. Remember we were talking about the Kalends and the Ides?
Since they were counting backwards from the beginning of March—excuse me—from the Kalends of March, they called it “doubling” the day six days prior to the Kalends of March. Or if you really want to get technical, “ante diem bis sextum Kalendas Martii.”
Bis sextum literally translated to doubling or splitting of the sixth day. Hence, leap years were known throughout the Middle Ages as “bissextile years.”
When Roman dating was replaced by the trusty 1-31 system, Leap Day was moved from February 25th to February 29th. Today, even though February is the 2nd month, we continue the 2000 year-old Roman tradition of placing the intercalaris at February’s end.
In simple English:
“When there is the double sixth day before the first day [of March], it matters not whether a person was born on the first or on the second day, and afterwards the sixth day before the first [of March] is his birthday; for those two days are regarded as one, but the second day is intercalated, not the first. And so he that was born on the sixth day before the first [of March] in a year in which there is no intercalation has the first day as his birthday in a leap year. Cato is of opinion that the intercalated month is an additional one, and he takes all its days for a moment of time, and Quintus Mucius assigns it to the last day of the month of February. But the intercalated month consists of twenty-eight days.”
–translation from Institutes and History of Roman Private Law with Catena of Texts, Salkowski & Whitfield
“Cum bissextum kalendas est, nihil refert utrum priore an posteriore die quis natus sit, et deinceps sextum kalendas eius natalis dies est, nam id biduum pro uno die habetur; sed posterior dies intercalatur non prior: ideo quo anno intercalatum non est sexto kalendas natus, cum bissextum kalendas est, priorem diem natalem habet. 1. Cato putat, mensem intercalarem additicium esse, omnesque eius dies pro momento temporis observat, extremoque diei mensis Februarii attribuit Quintus Mucius. 2. Mensis autem intercalaris constat ex diebus viginti octo.” –D. 50, 16, 98
[published Feb. 28, 2008]