What is "silbannacus"

Mar. Silbannacus is a mysterious figure believed to have been a usurper in the Roman Empire during the time of Philip I (244-249), or between the fall of Aemilianus and the rise to power of Valerian (253).

Silbannacus had been known only from a single coin, an antoninianus reputedly found in Lorraine, which is now at the British Museum. This coin has an obverse with the portrait of the usurper and the legend IMP MAR SILBANNACVS AVG (Imperator Mar. Silbannacus Augustus), the reverse shows Mercury holding a Victoria and a caduceus, with VICTORIA AVG (Augusta Victory) as legend. The name Silbannacus shows a Celtic origin, the "-acus" suffix; given the location of the coin, Silbannacus could have been a military commander in Germania Superior. As the coin was dated to Philip the Arab age, it is possible he revolted against Philip, with his revolt ending under Emperor Decius, since Eutropius (ix.4) reports of a bellum civile suppressed in Gaul during this emperor rule.

A second antoninianus has been published in 1996, bearing the shortened legend MARTI PROPVGT (To Mars the defender). According to the style, the coin was coined in Rome; since the shortened legend is present on Aemilianus coins, in 253, Silbannacus might have prevailed here during the march of Valerian on Rome. An interpretation of this facts leads to Silbannacus being an officer who was left in garrison in Rome while his emperor, Aemilianus, left to face his rival Valerian. After the defeat and the death of Aemilianus in September 253, Silbannacus would have tried to become emperor with the support of the troops confined in Rome, thus controlling the monetary workshop, before being quickly eliminated by Valerian and his son Gallienus.