Comment by zokier

Also: March is named after the Roman god of war, Mars.

This is because March is when they would begin to mobilize armies for campaigns. The timing is chosen by when winter wheat will be ready for harvest, so soldiers will have nearby high-calorie foot to pilfer while on campaign.

One tricky part of pre-industrial armying is that you can mostly only bring what food you can carry. Things that carry food (e.g. donkeys) require food themselves. So then you have to bring feed as well, which requires more donkeys… etc.

Instead, they would “forage” local areas. If they got there too soon, there is nothing en masse to take!

I've read that not only March was the first month, but the number of months was only ten: winter months did not need to be counted because there was no agricultural work to be done (which was the primary purpose of the calendar). So after the tenth month there was a strange unmapped period.

The first article in this blog post series has a little section talking briefly about this history, and there's a representation of this that I think sheds a lot of light on the original design. See the heading "Side-Note on Month / Day Determination" in the below link [1].

Displaying the months like the following helps see the regularity at a glance. Columns 1, 3 and 5 are the long months, others being shorter:

  +-----+-----+-----+-----+-----+
  | 31  | 30  | 31  | 30  | 31  |
  |  I  | II  | III | IV  |  V  |
  | MAR | APR | MAY | JUN | JUL |
  |-----+-----+-----+-----+-----+
  | 31  | 30  | 31  | 30  | 31  |
  | VI  |VII  |VIII | IX  |  X  |
  | AUG | SEP | OCT | NOV | DEC |
  +-----+-----+-----+-----+-----+
  | 31  |28/29|
  | XI  |XII  |
  | Jan | FEB |
  +-----+-----+

> To a person who natively thinks in Roman numerals, remembering that the short months are: II, VII, XII, along with IV & IX would be much easier than the way us modern folks have to memorise it.

[1] https://www.benjoffe.com/fast-date

> explains why the month names have offset to them (sept, oct, nov, dec)

Everything now makes sense, I always wondered why September was the nine month with a 7 prefix.

I thought Sept, Oct, Nov, and Dec were shifted by the addition of July (Julius) and August (Augustus)?

> not completely coincidentally, March was also the first month of the year in many historical calendars.

And often the last month too. The early modern English calendar began the year on March 25.

This is coincidental in relation to the offset in the names of the months. The Romans started their year in January just like we do today.

(Though in a very broad sense, it's common to begin the year with the new spring. That's the timing of Chinese new year and Persian new year. I believe I've read that the Roman shift two months backward was an administrative reform so that the consuls for the year would have time to prepare for the year's upcoming military campaigns before it was time to march off to war.)