A nice piece with 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 10 rows of bricks, with open gate, in the rim legend:
PROVIDEN-TIAE CAESS; in the segment TRhalf moonAL;
Bronze, diameter 18 x 20 mm, weight 3.18 g, axis 6 h.