A very nice, well struck piece.
Obverse: emperor's head in laurel wreath, to the right, in the rim legend:
ANTONINVS PIVS AVG BRIT;
Reverse: Mars standing left, holding olive branch, shield and spear, surrounded by legend:
MARTI PACATORI;
Silver, diameter 19 x 18 mm, weight 2.96 g, axis 6 h.