Very rare type (R4)! Camp-gate follis of Crispus (317-326 AD), Cyzicus mint, Roman Empire

FL IVL CRISPVS NOB CAES, diademed, draped and cuirassed bust left / PROVIDENTIAE CAESS, camp-gate with a door and two turrets, SMKD in exergue. 19mm, 2.9 grams. Cyzicus mint, RIC 46 (rated R4 - extremely rare), minted 326 AD.