In 66 AD, as Thrasea faced an almost certain death sentence, Arulenus Rusticus had offered to dissent and save him. No, Thrasea had said, it is too late for me. But there was still time, he had said to that courageous young man trying to save him, to think about what kind of politician he would be.

Rusticus would go on to raise a son who in turn would have a son who by and large proved that faith to be well founded. He would also prove, it seems, how often history hinges on small events.

Junius Rusticus, the grandson of Arulenus, was born around 100 AD, less than a decade after the murder of his grandfather. He would become the tutor who introduced Marcus Aurelius to Stoicism and helped form, in so doing, the world’s first philosopher king—the kind of leader who was the opposite of the men Arulenus had bravely stood against.

It would have made sense for Junius to want to turn away from this violent world, to hide in his books and in theories. We are told by one ancient writer that there was a part of Junius that would have been content to be a “mere pen-and-ink philosopher,” that he would have liked to stay at home and compose his theories in peace. But the sense of duty—instilled by the example of his grandfather, as it had been for Cato—called him to higher things.

It’s an example that should challenge every talented and brilliant person: You owe it to yourself and to the world to actively engage with the brief moment you have on this planet. You cannot retreat exclusively into ideas. You must contribute.

Junius, for his part, became a soldier and a general. In his early thirties, he was a consul under Hadrian. At some point he met Arrian, who had studied under Epictetus. It’s perfectly possible, modern scholars like Donald Robertson speculate, that Junius himself attended Epictetus’s lectures and wrote his own notes of what the great sage taught to students.

In any case, it would be a personal copy of Epictetus’s sayings that made its way from Junius’s library directly into the hands of a young Marcus Aurelius and changed the course of a man’s life.

A book given. A book read. Such a simple exchange, but done between the right two people at the right time—as it was here—can be enough to change the world.

At some point in the boy’s early twenties, Junius became Marcus Aurelius’s official tutor. It was, from the looks of it, a transformative period of study. As Marcus would later reflect, he learned from Junius matters big and small, from how to carry himself with dignity to how to write clearly and effectively.

“From Rusticus,” he reflected later in life,

I learned to become aware of the fact that I needed amendment and training for my character; and not to be led aside into an argumentative sophistry; nor compose treatises on speculative subjects, or deliver little homilies, or pose ostentatiously as the moral athlete or unselfish man; and to eschew rhetoric, poetry, and fine language; and not to go about the house in my robes, nor commit any such breach of good taste; and to write letters without affectation, like his own letter written to my mother from Sinuessa; to show oneself ready to be reconciled to those who have lost their temper and trespassed against one, and ready to meet them halfway as soon as ever they seem to be willing to retrace their steps; to read with minute care and not to be content with a superficial bird’s-eye view; nor to be too quick in agreeing with every voluble talker; and to make the acquaintance of the remembrances of Epictetus, which he supplied me with out of his own library.

From Junius, Marcus Aurelius learned all that Seneca was supposed to but failed to impart to Nero. Indeed, it’s a remarkable parallel. Nero had been attached to Seneca as a teenager, after the death of his father. Marcus began to study with Junius at age twenty-five, after the death of his mother. And when Nero became emperor, Seneca was drawn into more serious governmental affairs. In 161 AD, when Marcus became emperor, Junius was drawn into the role of magistrate and advisor. He, like Seneca, would go on to serve as consul.

Unlike Seneca, Junius seemed to be willing to deliver hard truths to his pupil. Marcus relates that he was “often upset with Rusticus,” but the teacher and student always reconciled. It’s a credit to both of them that Marcus was able to say he never became so angry with Junius’s criticism or methods that he did something he later regretted.

Nero had been a truculent student, a boy who was biding his time so he could do whatever he wanted when he got his power. The respect he had had for Seneca when he was young transmogrified with time into a kind of resentment and disgust. Seneca seemed to be willing to go along with this, to say his piece and hope it landed, and was otherwise unalarmed enough to allow Nero to get that power he so craved.

Marcus, on the other hand, was eager to learn and remained so for the rest of his days, even when the power dynamic between him and his tutor shifted. In the Historia Augusta, we’re told he greeted Junius with a kiss, always, and honored him before anyone else on his staff. He sought counsel in private and in public, and genuinely revered his teacher, to whom he considered himself a “disciple.” Rusticus had managed to do the thing that so few teachers manage, even with lowly pupils: He reached Marcus Aurelius.

Plutarch would talk later talk about how many politicians sought to govern as an exemption from being governed by others. Perhaps what made Marcus so special was that he seemed to place an advisor and a philosopher like Rusticus above himself, despite the fact that his power as emperor was nearly absolute. Why did Marcus remain good while so many other rulers have broken bad? His relationship and deference to a wise, older man like Rusticus explains a lot of it.

Almost immediately after Marcus became emperor, Junius was given major roles serving the state. In 162 AD, he served his second term as consul (almost thirty years after his first). For five years, he was urban prefect, essentially the mayor of Rome, supervising its police, legal enforcement, public works, and the city’s food supply. Given the vast corruption that had been endemic in Rome, this was a position of immense responsibility and trust. By all accounts, he acquitted himself honorably.

It would also put Junius on a collision course with an event that would, unfortunately, define his legacy for most of history. In 165 AD, a seemingly minor court case came to Junius’s desk. A Christian philosopher named Justin Martyr and a Cynic philosopher named Crescens had become involved in some sort of nasty dispute that had spilled out into the streets. Denounced by Crescens, who accused these Christians of being atheists, Justin and six of his students were charged and brought in to face questioning.

Justin had in fact studied under a Stoic teacher in Samaria but left the school in favor of the burgeoning Christian faith. Many of Justin’s writings would evoke similarities between the Stoics and the Christians and he may well have been familiar with Junius’s own philosophical work. He quite reasonably expected a favorable ruling from his Stoic judge. As a devout Christian, he knew that a century before, Seneca’s brother had fairly judged and and freed Saint Paul in Corinth.

But this was Rome in a very different time, and Rusticus was not simply a pen-and-ink philosopher. His job was to protect the peace. These Christians refused to acknowledge the Roman gods, the supremacy of the Roman state. That was crazy, disruptive, dangerous. Wasn’t Rusticus’s job to enforce the laws? To prevent these kinds of things from happening? And, perhaps, with Marcus away at the front and no one to check him, Rusticus was a little lost in the sway of his own power.

In her 1939 novel about Christianity in ancient Rome, written as fascism was crushing religious minorities in Europe, Naomi Mitchison has a Stoic philosopher, Nausiphanes, attempt to explain this collision course between the Stoics and the Christians. “[The Christians] were being persecuted,” he says, “because they were against the Roman state; no Roman ever really bothered about a difference of gods; in religious matters they were profoundly tolerant because their own gods were not of the individual heart but only social inventions—or had become so. Yet politically they did and must persecute: and equally must be attacked by all who had the courage.”

We think we are doing the right thing. We think we are protecting the status quo. We do terrible things in the process.

The proceedings of the trial, and its all too modern undertones, are recorded in The Acts of Justin. Rusticus gets right down to business, demanding an account of how Justin is living. Is he a Christian?

Yes. Yes, I am, he says, admitting that he knows his beliefs are seen as a threat by the powers that be. That power is not Rusticus, but the empire he represents. Even so, Rusticus seems to take personally Justin’s claim that that it is the Romans who “hold fast in error.” “Are the [Christian] doctrines approved by you, wretch that you are?” Rusticus demands, and their encounter spirals out of control from there.

As pride goeth before the fall, contempt goeth before injustices and moral failings.

Seneca had written his famous essay On Clemency to Nero in 55–56 AD. It’s likely, given how Nero turned out, that Rusticus was not a big admirer of Seneca’s philosophy. Yet in this case, the thrust of that essay—about how the decisions that the powerful make in regard to the powerless define who they are—was desperately relevant. Here, Rusticus controlled the full weight of the Roman legal system. Justin was just a small man, one man dissenting against a widely held belief. His example mattered very little. He could have been allowed to go free.

He deserved mercy. Most everyone does.

Rusticus was too frustrated to give it. He was baffled by Justin’s faith, by his firm belief in something that the Roman system did not countenance. That’s why Justin was sitting in court before Rusticus in the first place.

“Listen,” Rusticus says, “if you were scourged and beheaded, are you convinced that you would go up to heaven?” Justin replies, “I hope that I shall enter God’s house if I suffer that way. For I know that God’s favor is stored up until the end of the whole world for all who have lived good lives.”

Marcus said that from Rusticus he had learned “to show oneself ready to be reconciled to those who have lost their temper and trespassed against one, and ready to meet them halfway as soon as ever they seem to be willing to retrace their steps.” Where was that readiness with Justin? How much better would Rusticus have come off if he had managed to muster it?

He gave Justin a chance to repent, to submit to the law and go on his way. Justin didn’t have to mean it. He just had to do as every other Roman was expected to do. “Now let us come to the point at issue,” Rusticus said, “which is necessary and urgent. Gather round then and with one accord offer sacrifice to the gods.” The punishment for not doing so would be the same as for any Roman who dared impiety, who spurned the gods whose favor the empire believed it needed.

He was presenting Justin with the same choice offered to Agrippinus, to Cato, to Thrasea, to Helvidius. Go along to get along. Thrasea had faced it, had a chance at reprieve, but refused even help from Arulenus, Rusticus’s grandfather. Now, years later, the roles were reversed. It was not a tyrant demanding obeisance from a Stoic. It was a Stoic demanding it of a Christian.

This time, the Christian would be the brave one. “No one who is right thinking stoops from true worship to false worship,” Justin replied. And in so doing, chose to die for what he believed in rather than compromise and live.

Holding the immense power of the state in his hands, Rusticus chose to use it. “Let those who have refused to sacrifice to the gods and to obey the command of the emperor,” he ordered, “be scourged and led away to suffer capital punishment according to the ruling of the laws.”

In the name of Marcus Aurelius, at the order of Rusticus, this poor man was sent off to be cruelly beaten, whipped until the skin was torn from his body, and then beheaded.*

It would be a stain on two otherwise flawless reputations.

Even if Justin had been totally and indisputably wrong on this matter of religion, might the Stoics instead have considered that idea of sympatheia, which dated back to Zeno and Chrysippus? How could they have forgotten that we are all part of one large body, each with our own role, our own part to play? Marcus Aurelius would write beautifully that even the misinformed, even the selfish, even the shameless and stupid fit in that equation, and that we shouldn’t be surprised when we meet them. It would have been an idea he and Rusticus had discussed countless times.

Was a world of one hundred percent agreement on anything possible? Wasn’t it inevitable that some people would dissent, particularly on matters of religion? What was so shocking about the existence of the occasional heretic? What if—gasp—the heretic knew something you didn’t? What if most people, even the disruptive ones, were genuinely sincere in whatever they were doing?

Okay, Rusticus might have told himself as he presided over Justin’s trial, this man is one of those people who must exist in the world. Let me slap him on the wrist and let him go. But he didn’t. He was too lost in the black-and-whiteness of the legal case in front of him: Justin was refusing to comply with sacrificial ordinances, a daily practice in Roman life. This was civil disobedience and the law was clear. So he ordered one of the most famous executions in Christian history in 165 AD.

But only in retrospect.

This “martyrdom” was barely notable at the time. Rome was in the middle of the Parthian War and a conflict with Germanic tribes on the border was bubbling up. A plague was ravaging the empire. Millions would die. A death sentence for one lawbreaker would not seem like the kind of thing that history would remember.

History is like that. Just as the unremarkable decision to hand Marcus Aurelius a book would have outsize consequences, so too would this tiny case, which probably seemed at the time to be utterly indistinguishable from hundreds of others.

Just as it did not occur to the Stoics to question the institution of slavery, true religious freedom was an utterly inconceivable concept. But to martyr oneself for one cause, to refuse to compromise even under the threat of death? This should have been at least begrudgingly respected by someone as well versed in Stoicism as Rusticus.

Sadly, he could not do so. All he saw was a threat to the public order, a threat to his power. It was, ironically, the same thing that had motivated a paranoid emperor to kill Rusticus’s grandfather.

Duty-bound, Rusticus had done what he believed he had needed to do. Justin Martyr, the same. For the former’s failure to see a bigger picture, he would be a villain to millions of Christians for the rest of history. The latter, the victim, inspires the persecuted to this day.

In 168 AD, Junius left his position as urban prefect. Within two years he would be dead. Even as Marcus waged a brutal war hundreds of miles from Rome, he took the time to order the Senate to confer honors over his longtime teacher and friend, with whom he’d closely spent nearly half of his life. The Historia Augusta says that statues to Rusticus were placed around Rome—honoring a man not given to arguments, spectacles, or sermons, but only to the training of his character and public duty.

But the real monument to Rusticus—outshining even his own infamous court case—would be found in the life of the student he trained, the Stoic who would, finally, be king.