When I have issues with historians, I ask: "Excuse me, mate, were you there? No? Well, shut the fuck up then."

Sources:

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Brauer, George C. The Young Emperors, Rome, A.D. 193-244 (1967)

Dio, Cassius. Roman History, Book 79 (3rd century)

Dunstan, William E. Ancient Rome (2010)

Gibbon, Edward. The History of the Decline and Fall of the Roman Empire, Volume I (1776)

Goldsworthy, Adrian. How Rome Fell: Death of a Superpower (2010)

Hekster, Olivier. Rome and its Empire, AD 193-284 (Debates and Documents in Ancient History) (2008)

Herodian. History of the Empire from the Death of Marcus (3rd century)

Spartianus, Aelius, et al. Historia Augusta (3rd century)

Swan, Peter Michael. The Augustan Succession: An Historical Commentary on Cassius Dio's Roman History, Books 55-56 (9 B.C.-A.D. 14) (2004)