Constantine I. AE Follis. Trier. 307-308 AD. 

IMP CONSTANTINVS PF AVG, laureate, draped, cuirassed 
bust right, seen from the back.
MARTI PATRI PROPVGNATORI, Mars, wearing only helmet 
and chlamys, advancing right, holding transverse spear 
and shield. 

S-A across fields. 
Mintmark PTR. 

RIC VI Trier 778. Rare. 

With permission of Roma Numismatics, Apr, 2010