Did you ever wonder why October is called October? The prefix Octo means eight, but October is the tenth month. And when you think about it, November sounds like it should refer to the ninth month, en December seems like it should be the tenth.
The answer is that there used to be only ten months in a year:
In this calendar, which is said to have been invented by Rome’s legendary founder Romulus in about 700 B.C., October is number eight, November is the ninth month and so on. It’s amazing that almost all of the months’ names are still the same today, except for Quintilis and Sextilis.
If you feel that July and August are missing, that’s because they weren’t added until centuries later, by Julius Caesar and Augustus Caesar, respectively.