Constantius II. 324 - 355 AD. AE3. 23.5 mm. Rome mint, struck AD 350. 

D N CONSTANTIVS P F AVG, laurel and rosette-diademed, draped and cuirassed bust right, holding globe. A behind head.
GLORIA ROMANORVM, emperor, holding spear, on horseback galloping right, fallen enemy, wearing Phrygian helmet before the horse. 

Star in upper right field.
Mintmark RB. 

RIC VIII Rome 199.
Rated R3.

Note: The difference between RIC 196, 199 and 205 is the size. 
RIC VIII Rome 196 = 25-26 mm
RIC VIII Rome 199 = 23-25 mm
RIC VIII Rome 205 = 22-24 mm

With permission of Naville Numismatics auction 4, Lot 184, Dec. 2013