A nice piece. Patina, tarnish.
Obverse: bust of the emperor in radial crown, armor and paludamentum, to the right, in the rim legend:
IMP C VAL DIOCLETIANVS AVG;
Reverse: Emperor receives Victoria from Jupiter, surrounded by legend:
CONCORDIA MILITVM, in field A, in section XXI;
Bronze, diameter 21 x 22 mm, weight 4.1 g, axis 12 h.