Martialis is a late title of Juno especially honored by the third
century CE Emperor Trebonianus Gallus, who was known for his cowardice and bad
luck in battles; he only reigned three years before being murdered by his own
soldiers. Juno Martialis appears on coins of his short realm. The epithet Martialis,
which is literally "of or belonging to Mars", can also be taken as
"Warlike", but the depictions of Juno Martialis do not seem to bear
this out. On the coins She is shown enthroned, with scepter and orb or ears
of grain, or seated beneath the dome of a little temple (which looks like nothing
so much as a small carousel) with what may be a peacock, Her sacred bird, or
flanked on one side by birds and on the other by some sort of jars. She may
represent Juno as the virgin mother of the god Mars, and by extension she may
then be a Goddess of Childbirth.
During the short reign of Trebonianus a pestilence swept through
the region, and it might have been thought that Juno as a Goddess of the sky
and air could have some effect on the disease which seemed to be "in the
air" (for wont of an understanding of the way germs work); and in Her guise
as a warlike Goddess (if She is indeed warlike), She may have been thought especially
powerful in fighting off the plague.
Or Juno Martialis may be a Goddess of the month of March (which
would relate Her back to Mars anyway, as March is named for the Roman War-God
since it was the beginning of the war season), for She had a festival on March
7th, which may have commemorated the dedication of Her temple in the Campus
Martius, the old "Field of Mars" down by the Tiber.
She is sometimes equated with Juno Perusina, as
Perugia was where Emperor Trebonianus Gallus came from, and as such is called
Juno Martialis Perusina by modern scholars.