March named for Roman god of war & fertility: Mars

Statuette of Mars Ultor
Originally uploaded by Taifighta

Mars was the Roman god of war, the son of Juno and Jupiter, husband of Bellona, and the lover of Venus, says Wikipedia.

He was the most prominent of the military gods that were worshipped by the Roman legions. The martial Romans considered him second in importance only to Jupiter (their main god). His festivals were held in March (named for him) and October.

Initially Mars was a Roman god of fertility and vegetation and a protector of cattle, fields and boundaries and farmers.