This is a genuine Antoninianus coin from the emperor Postumus who ruled from 161 to 180 AD. The denomination of an Antoninianus had the value of 2 denarii and features the emperor wearing a radiate crown, indicating it was a double denomination. On the reverse it features Postumus standing left with a globe and a spear.
It is in incredible condition for being over 1700 years old with such crisp details and would be a fantastic addition to a numismatic collection.
A little bit of history:
Marcus Cassianius Latinius Postumus ruled as emperor of the splinter state of the Roman Empire known to modern historians as the Gallic Empire. The Roman army in Gaul threw off its allegiance to the current emperor Gallienus around the year 260, and Postumus assumed the title and powers of Emperor in the provinces of Gaul, Germania, Britannia, and Hispania (modern day France, Germany, Britain and Spain) . He ruled for the better part of ten years before he was murdered by his own troops.
Please look closely at the photos for the condition of the coin.
