Probus, AE antoninianus, AD 276-282, Ticinum. 

VIRTVS PROBVS AVG, radiate, helmeted, cuirassed bust 
left, holding spear and shield.
MARTI PACIF, Mars walking left, holding branch, spear and 
shield.
I in left field, star in right field.

Mintmark QXXI. 

RIC V-2 Ticinum 509.