Caracalla AE18, 1 Assaria of Nikopolis ad Istrum. 

AV K M AV ANTWNIN, laureate, cuirassed bust right.
NIKOPOLIT PROC I, serpent encircling center leg of tripod. 

Varbanov 3003 var (bust type); AMNG 1604 subtype 1 var (ditto).

With permission of beastcoins.com, online store. Added Oct. 2011.