[stevetodd]

March coincides with the first month of the Jewish calendar.

https://www.chabad.org/library/article_cdo/aid/2164005/jewis...

It was also the first month of the Roman calendar until January and February were added.

https://en.wikipedia.org/wiki/Martius_(month)

[madcaptenor]

There's a weird parallel between the Hebrew and Gregorian calendars. In both cases, the historic "new year" is in spring (Hebrew Nisan, Gregorian March), perhaps to coincide with planting? And in both cases intercalation happens right before that, at the end of the year - the Hebrew calendar duplicates Adar, the month before Nisan, and the Gregorian has an extra day of February. (Historically this was February 24 happening twice, not an additional day numbered 29, which is a whole other story.) But in both cases the year number increments at a different time - Hebrew Tishri in the fall, Gregorian January in the winter - so the intercalation appears to happen at some "random" moment within the year.

[eru]

In March, the month of war, is also when Romans mustered their citizen levy of troops.