Caracalla, AE31 of Serdica, Thrace.

AVT K M AVP CEVH ANTWNEINOC, laureate head right. 
OVLPIAC CERDIKHC, Apollo Iatros, bearded, naked, standing 
front, looking left, resting on serpent-entwined staff in left 
hand and resting right hand on hip. 

Ruzicka 167; Varbanov 2151 (this coin).