Why does the year start in January?

The ancients were an inquisitive lot, a characteristic shown to best effect in works like Aristotle’s Problems (‘Why do sex-maniacs’ eyelashes fall out?’) and Plutarch’s Greek and Roman Questions. Among much else, Plutarch asked, ‘Why do Romans adopt the month of January as the beginning of the new year?’

He began by doing the maths: July used to be called Quintilis, ‘Fifth’ (subsequently named after Julius Caesar) and August Sextilis, ‘Sixth’ (named after Augustus), while September to December covered the Roman numerals seven to ten. So, since the year contained only ten months, March must have been the first. He concluded that, to stay roughly in synch with the solar year, each month must have been lengthened. However, Plutarch reported, there was another analysis: perhaps the year did in fact have its full quotient of months, and January and February were the 11th and 12th.

But he was not happy with either of these proposals. True, he said, Romulus, the founder of Rome, was a son of the war-god Mars, and may therefore have wanted March (named after his father) to be the first month. But the next king of Rome, Numa, was a lover of peace, and Plutarch suggested he might have preferred to readjust the calendar, creating a new first month called after Janus, a god of peace and farming. But even that was not satisfactory, Plutarch concluded: ‘In a cycle (Greek kuklos ‘circle’), there is no natural first or last; it is just a matter of convention’. So he opted for the technical answer: the first month was that which came after the winter solstice (21 December in our hemisphere), which ‘increases light and decreases darkness, and so makes a sort of natural beginning for mankind.