In AD 65, the elderly philosopher Lucius Annaeus Seneca was forced to commit suicide on the orders of the emperor Nero. He had once been the emperor’s tutor and adviser, though he had withdrawn into retirement when the true character of Nero’s reign became clear, and he had recently become rather too closely involved with an unsuccessful coup (quite how closely, we shall never know). He must have been expecting the knock on the door.

The knock came from the captain of a troop of praetorian guardsmen who had stationed themselves around Seneca’s house, just outside Rome. Ironically, the captain himself was also involved in the planned coup, but had decided to follow the emperor’s orders in order to save his own skin (“he was now adding to the crimes he had conspired to avenge,” as the Roman historian Tacitus tersely put it). After a brief interrogation, Seneca was told to end his own life, which he did only with great difficulty. He severed his arteries, but he was so old and emaciated that the blood hardly escaped; so he asked for the hemlock that he had stashed away for just that purpose, but that had little effect either. He died only when his slaves carried him into a hot bath and he suffocated in the steam.

While all this was going on, he had been offering words of encouragement to the friends who happened to be dining with him when the praetorians arrived (he was bequeathing to them, he claimed, the only thing he had left, and the best: “the image of his own life,” imago vitae suae); and he had been dictating to his secretaries, for future circulation, some last philosophical thoughts. His final words were to offer a libation to “Jupiter the Liberator.”

So Tacitus—probably the most acute analyst ever of the autocratic rule of the Roman emperors—described the scene in his Annales, half a century or so later; he was no doubt relying on some hard evidence (a few modern critics have even suggested an eyewitness account), but inevitably recasting it in his own terms. One of Tacitus’s favorite themes in the Annales is death and its corruption; he repeatedly stresses the idea that autocracy disrupted not only the natural rhythms of life but the processes of dying too. People died for the wrong reasons, in the wrong places, and in the wrong order. Children killed their parents. Funeral pyres were prepared before the victim had even breathed his last. In fact, Tacitus opens his narrative of Nero’s reign with the bleak, and significant, phrase: “The first death under the new Emperor….” The suicide of Seneca, as Tacitus tells it, can be seen as a prime example of how even dying had been corrupted.

That is partly because, try as he might, applying…