Diocletian AE Antoninianus ca. AD 286. Siscia mint. 

IMP C C VAL DIOCLETIANVS P AVG, radiate, cuirassed bust right.
VICTORIA AVGG, Diocletian and Maximianus standing facing
each other, clasping hands, Victory standing behind and 
between them, resting her hands on their shoulders.
Mintmark dot XXI dot A.

RIC V 281; Cohen 480. 
Rare. 

With permission of cngcoins.com, Feb. 2006.
Estimate: $200.