I was doing some things with larger numbers this week. Septillion through decillion large. Which got me onto how September’s name implies it is the seventh of something, but it’s the ninth month in the Gregorian calendar. October is not the eighth month, November is not the ninth month, and December is not the tenth month.
So how did we get here, misnaming our months?
The answer is actually pretty simple. In the ten-month, lunar-based Roman calendar, September was the seventh month of the year and was followed by October, November, and December. Then, when the Roman calendar was replaced by the Julian calendar in the first century BCE, no one thought, “hey…this doesn’t really follow anymore”. Or, more likely, no one listened to the pedants who no doubt raised the very logical question of why we were mis-numbering months.