Sponsianus is believed to have been a Roman usurper, who attempted to seize the throne during the 240's, likely during the rule of Philip the Arab. The sole evidence for his existence is a single aureus of dubious quality.
The sole evidence found for his existence was from a single aurei, found in 1713 in Transylvania, among coins bearing the inscription of Philip the Arab and Gordian III, bearing the inscription of Sponsianus. The numismatist Henry Cohen believed them to be "very poor quality modern forgeries". However, according to the ancient numismatist Wayne Sayles, as the usurpers and emperors of the time were often ephemeral, the lack of coins should not be seen as evidence that Sponsianus did not actually exist. The problems with the aureus are twofold: firstly, the obverse (face) side of the coin is "barbaric and strange" according to the findings of the Roman Imperial Coinage, and the reverse (tail) side of the coin appears to be a copy of a Republican denarius struck in 135 BC.
Based upon the location of the aurei, if it is legitimate, it would place Sponsianus' ruling period sometime in the 240's. It is believed that this would have taken place entirely within the rule of Philip the Arab (244-249 AD). Based upon the location of his aurei, he is believed to have staged his revolt in Pannonia.
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