Gratian AE3, Siscia.

DN GRATIANVS PF AVG, pearl diademed, draped, cuirassed bust right.
GLORIA RO-MANORVM, Emperor in military dress, advancing right, 
head left, holding labarum, dragging captive behind him.
left field: M
right field: star over F.
mintmark: Gamma SISC

RIC IX Siscia 14c, type xvi

AAH Sale on ebay.