We are all familiar with our calendar and it seems natural enough to us. But if you take a closer look at the calendar it is immediately obvious that there's something very odd about it. The months from September to December have names that mean seventh, eighth, ninth and tenth, but they are in fact the ninth, tenth, eleventh and twelfth months of the year.

We inherited the fundamentals of our calendar from the Romans, who initially observed ten months of lengths varying from around 20 to 35 days. The early months of the Roman calendar had romantic-sounding names. The first month was March, named after Mars, the god of war; next came April, either from Aphrodite, the Greek goddess of love, or from the Latin word aperire, signifying the opening out of flower buds; then May, named after Maia, the mother of Mercury; then June, named after Juno, the wife of Jupiter, king of the gods. After that the Roman calendar makers seem to have given up a bit, because they called the succeeding months Quintilis, Sextilis, Septembris, Octobris, Novembris and Decembris - meaning, respectively, the fifth, sixth, seventh, eighth, ninth and tenth months.

Initially the Roman year, as constituted by the city's first ruler, Romulus, consisted of just 304 days. A further 61 days, which fell during the winter, were regarded as not belonging to the calendar at all. Eventually Romulus's successor, Numa Pompilius, decided to tidy things up a little and added the months of Januarius - named after Janus, a god with two faces, one looking forward and one looking back - and Februarius, the month of cleansing. According to some accounts, Januarius was added at the beginning of the year and Februarius at the end. To avoid oversimplifying the calendar, Pompilius decided that in every second year there should be an extra month, known as Mercedinus, which was inserted <em>just before the end of February</em>. The last few days of February were moved the end of Mercedinus.

In the light of this kind of oddity it seems unremarkable that the Romans were prepared to accept the fact that their calendar had now been muddled up so that the sixth month had a name that meant the fifth, the seventh month had a name that meant the sixth, and so on. Fortunately for us all, Julius Caesar stepped in to straighten things out properly. He put February in its proper place, and evened out the number of days in each month so that there was no need for the ridiculous Mercedinus. OK, so there was still a mismatch between the names of some of the months and their positions in the year, but Caesar went some way towards sorting this out too by eliminating the month Quintilis and renaming it Julius, after himself. Later Augustus Caesar, who succeeded Julius, was honoured by having the following month named after him. At least now there were only four months whose names were embarrassingly at odds with their proper numbers.

It was unfortunate for Julius that he never really got to enjoy his new calendar, or the month that was named after him. He saw only one month of Julius, as he was murdered before the second one came around. In a suitably calendrical fashion Caesar was stabbed to death on the Ides of March - the Roman way of saying March 15.