Tacitus AE antoninianus. Serdica, AD 275. 

IMP C M CL TACITVS AVG, Radiate bust left wearing balteo across the chest, spear and aegis.
PROVIDEN DEOR, Providentia, holding two standards, standing 
right, facing Sol, holding globe, and raising right hand, 
standing left.

Mintmark KA dot gamma. 

Estiot 2398 var;  RIC V-1 197 var (bust type).

With permission of Numismatik Lanz Auction 117, Nov. 2003, lot 1188. Very rare.