Commodus (161–192 AD)

Marcus Aurelius spent twenty years on campaign and a lifetime writing Meditations - one of history's great works of Stoic philosophy, still in print, still widely read. He also failed to solve the one problem that undid everything he built: his son.

Commodus became emperor at eighteen and initially showed some promise - he ended his father's costly frontier wars and returned a war-exhausted empire to peace. But he had no appetite for governance and an increasingly consuming interest in the arena, fighting as a gladiator in the Colosseum against opponents carefully selected to lose. He renamed Rome after himself. He renamed the months. He declared himself the reincarnation of Hercules and dressed accordingly.

What's easy to miss beneath the spectacle is the question his reign actually poses. The Antonine dynasty had produced five consecutive capable emperors through careful adoption - choosing successors on merit rather than blood. Marcus Aurelius broke that chain by insisting on his biological son. Commodus was the result.

He was strangled in his bath on 31 December 192 AD by a wrestler sent by his own inner circle, who had concluded that their survival required his removal. He was thirty-one. The year that followed produced five emperors. The Pax Romana, two centuries of relative stability, was over.