It's the second specimen known of a completely ulisted issue of the Rome mint.
OBVERSE
IMPCONSTANTINVSPFAVG [IMP CONSTANTINVS P F AVG]; bust r., laur., dr., cuir.
REVERSE
MARTIP-ACIFERO [MARTI PACIFERO]; Mars, helmeted, in military dress, lunging l., r. holding olive branch, l. spear and shield. R in left field, F in right field. R*Q in exergue.
2,96gr 20mm
Lech reports another specimen with a double die link.
http://www.forumancientcoins.com/notinric/7rom-18.html