Serdica, Thrace. Caracalla. 218-222 AD. AE31, 5 Assaria. 

AVT K M AV..ANTONINOC, laureate, cuirassed, bearded bust right, 
seen from front, fold of cloak on left shoulder.
O-VLPIAC-CE-PD-I around, KHC in exergue, Emperor on horseback
galloping right, holding spear. Beneath horse's forelegs 
seated captive wearing Phrygian helmet, with hands tied behind back. 

Apparently unpublished. Not in Ruzicka's or Mouchmov's 
corpuses of Serdican coinage, nor in Varbanov, with 
seated captive below horse.

cf Ruzicka 346 (different obv. legend); Sofia 2333 (ditto); 
Moushmov 4870 var (spear).

Contributed by Imperial Coins, November 2009