It is tricky trying to pick out deranged rulers from contemporary historical sources. Some focus upon gossip, some have a political or social axe to grind. So, the emperor Justinian the Great, in the sixth century AD, is represented by his chronicler Procopius of Caesarea as being a shapeshifting demon. Justinian might be criticised for being suspicious (a quality any decent emperor perhaps ought to cultivate), vena; and perfidious; but this was the man who conceived of the ‘counterattack’ against the barbarian kingdoms who had occupied the western empire. The historian Tacitus disliked the autocratic Domitian, at a time when collective governance was still a tradition at Rome, portraying him as a conflicted individual, vicious and cruel. Yet, Domitian also proved a decent and far-sighted administrator. It all depended on how close you were to power I suppose.
Then there were the ‘accidental emperors’ those thrust into power, or who manoeuvred their way there, on the cusp of rebellion, crisis or desertion, and whom, it soon transpired, had made a bad life choice. Didius Julianaus, the banker who ‘bought’ the empire off the Pretorian Guard in the early third century AD, very soon regretted his investment as more capable men came calling in his loans. Maximinus Thrax, a military bruiser, supposedly the son of a low-life gladiator (a shocking overturning of the social order!), and the first fully proletarian emperor, was briefly raised up by his drinking pals in the Danubian legions before they realised their mistake.
There were a goodly number of princes gone wrong, youthful hopefuls who proved incapable, or cracked under the pressure of governance. Gaius Caligula, the Julio-Caludian golden boy, is the most famous example. It is debatable whether he was truly mad, or simply capricious. Much of what we know is clearly gossip, and yet… Suetonius describes how he purloined the temple of Castor and Pollux in the forum as the entrance hall of his grand new palace, connected to it by a viaduct, from which he showered money on the populace. Fiction? Perhaps, but the excavations of the 1980s revealed the foundations of a bridge-like structure. Another such was Nero, the classic example of one raised to power, provided with the best tutors, but who let it all go to his head. Not mad, just bad in this case, a clear case of a spoilt brat. Contemporaries were seemingly more shocked by his artistic and dramatic ambitions than his policies. He underwent the physical transformation one might expect of a ‘baddie’, recorded faithfully on his coins in a way that perhaps belies the claims of vanity, from the very image of Augustus, to a fat porker.
But not all the cut-throat and ruthless clawing of ones way up the political ladder produced monsters. The Pretorian Prefect Diocles gained the throne in the time-honoured way by hastening the demise of his predecessor Numerian in AD 286. Given the problems of the empire at this time is amazing that anyone should honestly want the office. Yes Diocles, who quickly Latinised his name to Diocletian, faced the overwhelming issues and may have bent but did not break under the weight. He reed the state, devolved power, and created the conditions for ‘Roman’ power to continue, one way or another until 1453, helping to erect the scaffolding of the middle ages. After 20 years he laid down his office and uniquely, retired to tend his market garden at Split.