Silbannacus is not mentioned in any contemporary documents and his existence was forgotten until the 20th century, when two coins bearing his name were discovered, the first in the 1930s and the second in the 1980s.

Based on the design of the coin and its silver content, Silbannacus was most likely concurrent with the reigns of Philip the Arab (r. 244–249), Decius (r. 249–251), Trebonianus Gallus (r. 251–253), Aemilian (r. 253), or Valerian (r. 253–260).

The two most prevalent ideas are the older hypothesis, that Silbannacus was a usurper in Gaul during the reign of Philip the Arab, at some point between 248 and 250, and the newer hypothesis, based on the design of the second coin, that Silbannacus was a briefly reigning legitimate emperor, holding Rome between the death of Aemilian and the arrival of Valerian.

[1] Another possibility is that Silbannacus is a misspelling of Silvannacus or Silvaniacus,[3][4] names derived from the Roman forest god Silvanus.

[5] If his nomen was Marcius, Craven considers it possible that he could have been related to Marcia Otacilia Severa, the wife and empress of Emperor Philip the Arab (r. 244–249).

Romans minted coins in large numbers, meaning that there only being a single known example made its authenticity, and the existence of Silbannacus, uncertain.

[3][4] This makes Silbannacus an emperor or usurper during the turbulent Crisis of the Third Century when the Roman Empire was plagued by both internal instability and external threats.

[4] The second coin was held in a private collection for many years after its discovery and its existence was not widely known until it was published by the French historian Sylviane Estiot in 1996.

[4] It was only with Estiot's paper that Silbannacus became widely accepted as a real historical figure, his existence now supported by two coins, rather than a single one.

In contrast to the many fully-bearded contemporary emperors, Silbannacus apparently did not have a full beard, but whiskers descending alongside the jawbone, and a beardless chin.

[2] Craven suggests 248 as the most likely year, placing a revolt by Silbannacus shortly prior to the uprisings of the subsequent usurpers Sponsian, Pacatian and Jotapian.

[1] These reconstructions are highly speculative: there are no known records of Germanic tribes threatening the Rhine frontier during the reign of Philip, and the ideas that Silbannacus was a commander or governor are as of yet baseless.

[8] If he ruled the capital, which would require support from the Roman Senate, Silbannacus may be counted as a legitimate, albeit ephemeral, emperor, rather than a failed usurper.