When Posidonius arrived in Athens sometime between 117 and 115 BC, he found the Stoa Poikilē firmly in the hands of Panaetius, who was by then an old man and a towering figure, not only in the Stoic school but also in the empire. Fathers from across the Roman ruling class—from senators to generals and even kings of distant provinces—had begun to have their children educated by philosophers. Where Panaetius had taught Rutilius a generation earlier in Rome, many of Rome’s richest and most powerful were now sending their most promising children to him in Athens to prepare them for entry into Roman life.
And yet even amid these star pupils from the Eternal City, the young Posidonius must have stood out for his brilliance. Sources portray him as a polymath with diverse interests in natural history, astronomy, meteorology, oceanography, geography, geology, seismology, ethnography, mathematics, geometry, logic, history, and ethics. Perhaps it was Panaetius, who had traveled widely on his fact-finding mission, who encouraged his young student to take his studies on the road. What we know is that after his time in Athens, the next large chunk of Posidonius’s life was spent studying in far-flung places from Italy, Sicily, Greece, and Dalmatia to North Africa and the Near East.
It cannot be said that the Stoics, like some philosophers, were interested only in their proofs or debates. Posidonius perfectly illustrates the curiosity, the fascination with the beautiful and complex world that surrounds us which defined Stoicism in the ancient world and continues today. You can and should be interested in everything, the Stoics taught, because you can and should learn wisdom from everything. The more you experience, the more you learn, and, paradoxically, the more humbled you are by the endless amounts of knowledge that remain in front of you.
As Posidonius traveled, his reputation grew as the greatest polymath since Aristotle. He measured tides in Spain and conducted ethnographic research on the Celts in Gaul. He was a keen observer and a lover of data—regardless of the discipline—and a diligent recorder of it all. He measured the circumference of the earth, the size and distance of the sun and the moon, created models of both the globe and the known solar system. The only constraint on his brilliance was the crude measuring tools of his age, which often skewed his calculations. Still, his ceaseless travel and unmatched curiosity dramatically increased the understanding of the known universe at that time.
It also got him outside, down in the dirt and out on the water. His classroom was the sky and the stars and the bustling marketplace, as it had been for Zeno, as it is for the child who can be fascinated even by an ordinary patch of grass. Posidonius lived, as Seneca would later write, as if the whole world was a temple of the gods.
Some geniuses are content to live entirely in their own heads. Many philosophies—filled with philosophers who no doubt see themselves as geniuses—subtly encourage this tendency. Epicureanism, for instance, which was resurgent in Posidonius’s time, encouraged its followers to turn away from the world, to ignore politics and the noise around them. Posidonius, thanks to the influence of Stoics like Diogenes and Panaetius, resisted the pull of this bubble and, like a good Stoic, also turned his intellect to politics and governance.
Indeed, his far-flung travels brought him in constant contact with Roman legions, legions that had been trained for Marius by his fellow Stoic and student of Panaetius, Rutilius Rufus. We see evidence from the fragments of his writings that Posidonius studied troop movements, the history of warfare, and the customs of local people, and even gathered intelligence about foreign powers, which he not only provided to generals but later used in his many books. He even wrote a manual on military tactics, a kind of Art of War, that was so detailed that it was considered too advanced for anyone but a general. In addition to becoming a repository of military tactics, he also had deep ethnographic insights gathered from the foreign territories, which generals like Pompey would seek from him for many years.
He was the complete man. An explorer. Strategist. Scientist. Politician. He was, then, a real philosopher.
At some point, though, every traveler must come home, which for Posidonius became Rhodes. Putting his study of politics into practice, he rose in the leadership ranks there to the highest civil position of prytany, presiding over the governing council in Rhodes while building up his philosophical school.
His political duties would bring him to Rome in 86 BC on embassy, but it was likely his curiosity and desire to study human beings that brought him to the deathbed of one of Rome’s worst strongmen, Marius. Marius was elected to his seventh consulship in late 87 BC, and seemed to think that his political power made him immortal. He could not have imagined that Posidonius would be one of the last faces he would ever see.
Delusional, tortured by dark dreams, wearied by a life of endless ambition and the creeping fear that it had all been for naught, Marius received Posidonius, a keen observer, who was repulsed by what he saw. A few days after the meeting, Marius died, convinced until the end that he would once again be leading troops in battle and expanding his conquests. As a Stoic, Posidonius must have noted—as Plutarch would—what a far cry this was from the peaceful passing of a philosopher like Antipater, who had spent his final moments counting the blessings of his voyage through life.
It’s a timeless question: If you actually knew what “success” and “power” looked like—what it did to the people who got it—would you still want it?
Posidonius’s later writings are filled with firsthand observations about the costs of ambition and insatiable appetites. In one of his histories, he writes of a philosopher named Athenion, who had designs on becoming a tyrant in Athens. It must have struck Posidonius how easily people can be corrupted and cut off from virtue, for here was a man with similar training who had abandoned his genius to marry a prostitute and depended on the mob for his own political advancement.
In another account of a revolt in Sicily, he spoke of a Damophilus, “a slave of luxury and malpractice, driven through the country in four-wheeled chariots at the head of horses, luscious attendants, and a concourse of bumsuckers and soldier-slaves.” Almost with a sense of satisfaction, Posidonius tells us how Damophilus came to a violent and painful end at the hands of his slaves. We can imagine Posidonius expecting a similar comeuppance for Apicius, the gluttonous and greedy monster who was responsible for bringing his friend Rutilius Rufus up on a false charge.
What linked all these historical cases together in Posidonius’s mind was a deficiency of character. “Robbers, perverts, killers, and tyrants,” Marcus Aurelius would later write, “gather for your inspection their so-called pleasures!” Posidonius had actually done that, been in the room with Marius, inspected would-be tyrants and killers up close just as he had observed the tides and the movements of the planets.
From this he was able to pass along insights that were just as valuable as his scientific ones: Be wary of ambition. Avoid the mob. Luxury, as much as power, rots. From Seneca, we get Posidonius’s final judgment on Marius: “Marius commanded armies, but ambition commanded Marius.” Seneca paraphrased, “When such men as these were disturbing the world, they were themselves disturbed.”
After Panaetius’s death in 109 BC, Posidonius would leave Athens for the last time, convinced that the people had become simply “a mindless mob” (ochloi anoetoi). Posidonius probably didn’t think much better of the Romans, after what he had seen firsthand.
Rhodes, at once both isolated and still central to the flow of goods and ideas across the Mediterranean, was a perfect perch for this independent thinker. Posidonius worked on his histories and his theory of the human personality during this time, and they both reflect a more realistic and disillusioned appraisal of his fellow man—an assessment often shared by geniuses. But just as this view was settling in, Posidonius was visited by a bright light. In 79 BC, a young Cicero, then twenty-seven years old, and a kind of once-in-a-generation talent (like Posidonius), would make his way to Rhodes to study under the great man. Panaetius had his Posidonius and now Posidonius would have his own brilliant pupil, who in turn would lovingly refer to his teacher in his writings as “our Posidonius.”