Hi, I have a donate button, just reminding you of that in case you've recently come into a fortune and want to use it to help me get through the winter or whatnot.
I've been sick today so no particularly interesting things will go on in this post, but I will keep up with my usual talking about this history of months posts.
December is a number month (Decem = 10) and as such it's pretty boring.
The original Roman calendar was a 10 month year with a bunch of monthless days in the dead of winter. December was the 10th month of that year, hence the name. December had 30 days.
When January and February were added to the front of the calendar the changes involved in that reduced the days in December to 29.
In 46 BC Julius Caesar reformed the calendar again. With the exception of years divisible by 100 but not 400, it is the same calendar we use today.
Thus December grew to 31 days.
The Julian calendar added days to the ends of the month (after the ides) so the ides of December are calculated as if it were still a 29 day month (and thus fall on the 13th.)
Thus today, though within December, is notated as the 18 days before the Kalend of January (a.d. XVIII Kal. Jan.)