Probus AE antoninianus, Ticinum mint.

IMP C PROBVS PF AVG
Radiate bust left, wearing imperial mantle, holding
eagle-tipped sceptre.
MARTI PACIF, Mars walking left, holding branch, spear and 
shield.
I in left field, star in right field. Mintmark QXXI.

RIC V-2 Ticinum 507 var (fieldmark positions).
Rare.

Contributed by Charles, Jan 2013.