I'm pretty sure it's Gallienus based on that last photo, a tiny bit of the lettering indicates that. You can see I E N
Yes, its Gallienus, 253 - 268 AD, Mars reverse. Check to see if you can see in the reverse lettering "MARTI PACIFERO". That is the most likely candidate.
Gallienus for sure Perhaps something like this one: GALLIENUS Antoninianus OBVERSE: GALLIENVS AVG - Radiate head right. REVERSE: VIRTVS AVG, Virtus standing left, resting hand on shield & holding spear Struck at Mediolanum, 260-8 AD 4.10 gm., 22 mm RIC 534
Thanks guys! I believe you are all correct. It is 21mm(but its sides are worn) On the reverse, I can read 2 letters of beginning and the end, on the sides of each foot. On the left it reads V I , and on the right side it reads T I.