On the first of May in the year 305, a sixty-year-old man took off his cloak in front of his own army and told them he was finished. The cloak was purple, the one color no ordinary Roman was permitted to wear. He had worn it for twenty years, since the day his soldiers hoisted him onto a platform and called him emperor over the body of a man he had just killed to earn the title. What he did next has almost no equal anywhere in the history of power, and almost nobody remembers it.

Illness caught up with him near the end. He fell seriously sick in early 304 and disappeared from public view for months, recovering only partially. By the following spring he had decided, and unlike every emperor before him, he did not wait for death or a rival's blade to end his rule. He forced his reluctant co-emperor Maximian to resign the same day, in a separate ceremony in Milan, so neither man could use the other's continued authority as an excuse to reconsider. Then he sailed home to Dalmatia, to the palace he had already built for exactly this purpose, and began the work of turning an emperor back into a private citizen.

Three years into his retirement, the system he had built started coming apart. Rivals declared themselves emperor. Maximian broke his word and tried to reclaim power. In November 308 the surviving rulers gathered at Carnuntum, on the Danube, hoping the old man could talk sense back into the arrangement. According to the historian Aurelius Victor, when they asked him to return, Diocletian answered: "If you could show the cabbage that I planted with my own hands to your emperor, he would not dare suggest that I replace the peace and happiness of this place with the storms of a never-satisfied greed." He did not go back. The empire limped through another round of civil war, and Diocletian spent his last years in the palace he had built, never once returning to public power.

The obvious comparison is Napoleon. Napoleon abdicated once in 1814, was exiled to a small island off the Italian coast, escaped within a year, marched back into France, and gambled the whole project again at Waterloo before losing everything a second time and dying, guarded and bitter, on a rock in the South Atlantic. Schoolchildren across Europe can recite the outline of that story without opening a single book. Diocletian ran an empire on the edge of ruin for twenty years, built a system that outlived him by generations, resigned voluntarily at the height of his power, and spent his retirement growing cabbages until he died an old man in his own bed. Almost nobody outside a university history department could tell you his name.

The reason is straightforward once you sit with it. Diocletian is not really the point of the story. The rest of us are. Catastrophe makes a better story than restraint. An emperor who loses everything twice, who claws his way back for a hundred days out of sheer refusal to accept an ending, gives history the arc it already knows how to tell. An emperor who simply stops, who hands back what he built while he still holds it, denies the story its final act. We remember the fall because the fall carries its own drama inside it. The clean exit leaves nothing behind for anyone to dramatize, which is precisely why it worked, and precisely why it vanished from memory almost as completely as the man who chose it.

Readers who remember Newman's threshold or Grant's exit at sixty-two will recognise the shape of what follows here. A man who could see the whole arc of his own story before anyone else could, and got out at the right sentence instead of writing three more chapters nobody needed.

Every person who builds something worth having eventually faces a smaller version of Diocletian's spring morning. The business that could keep growing under someone else's hand. The title that could be handed over a year earlier than pride would prefer. Most of us choose the version of the story that keeps us in the leading role for as long as possible, and call it commitment. Diocletian chose differently, and got a vegetable garden and near total obscurity for his trouble.

Gibbon has been open on my desk for most of this week, which will surprise nobody who has seen how long that book actually runs. He reaches the cabbages eventually, and it is clear even through his very formal prose that he respected this particular emperor more than almost anyone else he covered in six volumes on the empire's decline. The idea worth sitting with is a simple one. The ending nobody remembers might be the one most worth choosing.

Until Sunday.