Probus (276-282 n. Chr.) Antoninian, Siscia - ex. Philippe Gysen

Very rare and sought after (at Siscia mint) greek letter KA mintmark.  Siscia predominantly used latin (not greek) mintmarks together with the latin XXI monetary reform mark. 

Greek letter KA and latin letter XXI mintmarks first appeared in 274 A.D. to mark Aurelian's reform of the antoninian denomination. The symbol KA ("K" in Greek = 20; A in Greek = 1; 'XX" in latin = 20, "I" in latin = 1) officially certified 5% silver content in coinage (1/20 = 5%).  

Obverse: IMP C M AVR PROBVS P F AVG

Radiate bust left in imperial mantle, holding eagle-tipped sceptre (scipio).

Reverse: ADVENTVS PROBI AVG / KA

Emperor on horseback left, holding sceptre and raising his hand, captive at his feet. 

Provenance: Paul Francis Jacquier Auction 46 lot no. 453 = ex Philippe Gysen collection