Constantine. AE half-follis. 310-311 AD. Trier. 

CONSTANTINVS AVG, laureate, draped bust right, seen from behind.
MARTI-CONSERV, Mars, helmeted, standing right, 
holding reversed spear and left hand resting on 
shield on ground. 

PTR in ex. 

RIC VI Trier 897. Scarce.

Courtesy of Roma Numismatics, Apr, 2010