As I found a new interest in 3rd century coins, the 4th century got neglected, so here is something to make up for the shift in focus:
CONSTANTINE II AE3 18mm 3g Follis/Nummus (VF, patina, scratches)
AV: CONSTANTINVS IVN NOB C; laureate draped cuirassed bust r.
REV: CAESARVM NOSTRORVM; VOT/V inside wreath
EXE: R eRwC in ligature Q Rome mint
REF: RIC VII Rome 231, rated R5, 320-321AD.
The interesting mintmark is the greek EROS in ligature, which is the counterpart of AMOR in latin, which in turn is ROMA backwards.
Not an unlisted coin, but as far as I could notice, quite scarce, at least scarcer than the ROMAE AETERNAE type w/ the same mintmark.