What you have is an AE4 (smallest of the bronze coins) of the Constantine dynasty or maybe a little later. The legend is worn/broken off, so all you have to go on is the portrait. This website may help somewhat:
http://www.romancoin.info/
Reverse I am pretty sure is the "Two soldiers with military standard" type, or GLORIA EXERCITVS.
http://www.romancoin.info/
Reverse I am pretty sure is the "Two soldiers with military standard" type, or GLORIA EXERCITVS.


























