A nice piece. Patina, tarnish.
Obverse: emperor's head in radial crown, to the right, in the rim legend:
GALLIENVS AVG;
Reverse: Fortuna standing left, holding rudder and horn of plenty, in rim legend:
FORTVNA REDVX, in the field S;
Bronze, diameter 20.5 x 22 mm, weight 3.2 g, axis 6 h.