Constantius II, AE3, Arles.

DN CONSTAN-TIVS PF AVG, pearl diademed, draped, cuirassed bust 
right, A behind bust.
FEL TEMP R-EPARATIO, soldier spearing fallen horseman who is
sitting on ground, arms up, wearing Phrygian helmet.

A in left field.
Mintmark PARL

RIC VIII Arles 120, rated scarce.

From Dane's collection, ex Tony Owens with many thanks, Nov. 2011.