A nice piece. Patina.
Obverse: emperor's head in laurel wreath, to the right, in the rim legend:
L SEPT SEV PERT AVG IMP X.
Reverse: Mars standing left foot on helmet, holding spear and olive branch, surrounded by legend:
MARTIPACIFERO
Silver, diameter 16 x 17.5 mm, weight 3.37 g, axis 12 h.