Constantine II, AE follis. Cyzicus. AD 325-326. 

CONSTANTINVS IVN NOB C, laureate, draped and cuirassed bust left.
PROVIDEN-TIAE CAESS, campgate, seven layers, two turrets, 
star abvove, no doors. 
Dot in left field.

Mintmark SMKA. 

RIC VII Cyzicus 52.