Constantine I AE Follis. 21mm. Rome mint, 318-319 AD.

Obv: CONST-ANTINVS AVG, helmeted, cuirassed bust right
Rev: ROMAE A-ETERNAE, Roma, seated right, holding shield 
inscribed XV in lap. P-R across fields.
Mintmark RP.

RIC VII Rome 146

Contributed by Jeff Clark at JAC Ancient Coins, Jan. 2001.