Valerian II, AE20 of Nicaea, Bithynia, 256-258 AD. 20.56mm - 4 gr.

Obv: P L KOR OYALERIANOC K, Bare-headed, draped bust right.
Rev: IPPARXOC NIKAIEWN, Hipparchus the astronomer seated left 
on cippus, globe on pedestal to left; countermark of a head left. 

SNG Von Aulock 7097 

With kind permission of Nemesis Ancient Coins on vcoins, Nov. 2011.