The Longest Year

You've heard about the leap year, of course - 366 days long. You may even be aware of the Hebrew and Arabic tradition of adding a 13th month to some years in their Lunar calendars. But did you know that one year more than two eons ago had 15 months and 445 days? It was 707 A.R.C. (Anno Romanus Civitas), better known to us as 46 B.C.; to the locals it was The Year Of Confusion.

This problematic year was actually the solution to another problem, that of coordinating the Roman calendar to the Solar year. Since it had only 355 days, the Roman calendar was off by at least 10 days each year. To compensate, Roman astrologers would add a 13th month, Mercedonius, to the year. Even that wasn't regular, however: Mercedonius had varying lengths depending on the will of the chief astrologer, and its placement in the year was not always at the end, but sometimes in the middle. There was also no regular plan as to which years would have Mercedonius added; sometimes it was every other year, sometimes every third, sometimes longer.

When Julius Caesar came to power in 707 (-46 to you and me) he immediately set about reforming the calendar. The Egyptian calendar was based on the Solar year and was the most accurate in the ancient World, so he designed his Julian calendar after it. The new Julian calendar had 365 days with a leap year every 4 years; this was considered sufficient to keep the seasons congruent to the months. Now the only problem was deciding when to start the year.

Traditionally, years had always begun on the Winter Solstice, the shortest day of the year. Unfortunately, the Roman calendar had gotten so far out of alignment that the year was now starting in late summer. Before standardizing the calendar for all eternity (he thought) Caesar wanted to move the start of the year back to the Winter Solstice. His solution was to add 3 months to the then-current year, 707 A.R.C.

The result was a year that had begun in late summer and would now end on the beginning of winter. What was worse was that Caesar had made this change in the middle of 707, when people had already planned the rest of their year and part of the next, so all plans now had to be recalculated. The last two months, Unidecember and Duodecember, were longer than any other months ever had been, and they were never used again.

The Romans believed that even numbers were bad luck, so only two of the 15 months had an even number of days - Februarius and Duodecember. The breakdown went as follows:

46 B.C. - 15 months

• Januarius - 29 days
• Februarius - 28 days
• Martius - 31 days
• Aprilis - 29 days
• Maius - 31 days
• Junius - 29 days
• Quinctilis - 31 days
• Sextilis - 29 days
• September - 29 days
• October - 31 days
• November - 29 days
• December - 29 days
• Mercedonius - 23 days
• Unidecember - 33 days
• Duodecember - 34 days

445 days total

Thus, 708 A.R.C. (45 B.C.) was the first year of the Julian Calendar. This would remain the standard calendar of Western civilization until the reforms of Pope Gregory in September 1752.