Very rare reverse type from Siscia's 2nd emmission. VIRTVS AVGVSTI is a much, much rare reverse type than VIRTVS PROBI AVG reverse with similar iconographic scene.
Obverse: IMP C M AVR PROBVS P F AVG
Radiate bust left in imperial mantle, holding eagle-tipped sceptre (scipio)
Reverse: VIRTVS AVGVSTI / Δ / XXI
Emperor on horse to right spearing enemy.
Bilon, diameter 20,9 mm, weight 3,83 g.
Great provenance: Paul Francis Jacquier Auction 46 lot no. 439 = ex Philippe Gysen collection = Ex Numismatic Fine Art (NFA) BBS Summer 1993, lot 617