Mars was also the god of agriculture, which was the main reason the first month was named after him, as that was when the sowing of fields started as well as war campaigns usually starting around that time of year as well.

I forget, but was Intercalaris not a month in the Roman calendar too? If I remember correctly, they had a leap month that they would implement some years to realign the calendar, but I forget if that was Intercalaris or the one that starts with an M. I always forget what it’s called.