Probus, Siscia mint, officina 6, 7th emission, 280 AD.,
Æ Antoninianus (22-24 mm / 3,56 g),
Obv.: IMP C M AVR PROBVS AVG , radiate, cuirassed bust of Probus right.
Rev.: CONCORD MILIT / VI / XXI , emperor standing right, clasping hand of Concordia.
RIC 651 Bust Type F. Also Alföldi type 26, n° 75 .
thanks to Martin Griffith for the detailed reference