A nice piece with fairly well preserved details.
Obverse: bust of Caesar in armor and paludamentum, wearing a laurel wreath, left, in the rim legend:
CONSTANTINVS IVN NOB C;
Reverse: camp gate of 8 rows of bricks, with open gate, surrounded by legend:
PROVIDEN-TIAE CAESS; in section SMANTS;
Bronze, diameter 18 x 20 mm, weight 3.66 g, axis 11 h.