Constantine I. AE Follis. 305-307 AD. 

FL VAL CONSTANTINVS NOB C, laureate, draped, cuirassed bust right,
 seen from the back

GENIO POPV-LI ROMANI, Genius standing left, tower on head, loins draped, holding patera and cornucopiae. 

S-F across fields. 
Mintmark PTR. 

RIC VI Trier 669b. Scarce.

With permission of Roma Numismatics, October, 2009