Here is a better picture of the coin.
Constantine I
A.D. 312- 313
22mm 3.8gm
CONSTANTINVS P AVG; laureate & cuirassed bust right.
ROMAE RESTITVTAE; Roma, helmeted, seated left, holding branch in right hand and globe in left; star in left field.
In ex. PLN
RIC VI London 273
This coin commemorates the defeat of Maxentius and recovery of Rome.