Here is an early issue of the MARTI type, struck shortly after Constantine defeated Maxentius. This type from Rome is more scarce than from the other mints.
Constantine I
AD 312- 313
22mm 3.3gm
IMP C CONSTANTINVS P F AVG, laureate and cuirassed bust right.
MARTI CONSERVATORI, Mars standing right, head right; right leaning on reversed spear, left on shield.
In ex. RP
RIC VI Rome 307
I have this coin in my collection since a few years and i classified it as RIC 307 var (unlisted officina). I supposed that the description in RIC was inaccurate, but after seeing your coin Victor i was wrong.
your example has much nicer engraving
Yes Victor, but also Mars il looking left with inverted position of shield and spear.
yes, I saw that. It is interesting, though, that it seems to be a more skilled engraver, but he seems to have made a simple mistake and engraved his image backwards. I mirror imaged the pic which makes it look like the normal type.