this coin from Ticinum has a seen from rear bust type and is fairly rare.
Constantine I
A.D. 320- 321
19mm 3.0gm
CONSTAN-TINVS AVG; Laureate, draped and cuirassed bust, seen from rear.
DN CONSTANTINI MAX AVG surrounding wreath enclosing VOT XX
in ex. ST
RIC VII Ticinum 141