There’s a little-known passage about Stoics and other philosophers in Roman political history in the 34th Oration of Themistius, from the 4th century AD, entitled In Reply to Those who Found Fault with him for Accepting Public Office:
The emperor [Theodosius] has shown those who are now alive something they no longer expected to see: philosophy passing judgment in union with the highest power, philosophy broadcasting inspired and action-oriented precepts that up to now she has merely been proposing in her writings. Future generations will sing the praises of Theodosius for his summoning of philosophy to the public sphere, just as they will praise Hadrian, Marcus [Aurelius], and Antoninus [Pius], who are his ancestors, his fellow citizens, founders of his line. Theodosius was not content merely to inherit the purple from them; he also brought them back into the palace as exemplars after a long lapse of time and set philosophy by his side, just as they had done.
Neither the Persian Cyrus nor Alexander the Great could reach this level of distinction. Alexander deemed his guide Aristotle worthy of many great honors and peopled Stagira for him, but he did not give the philosopher a role in the exercise of that massive power of his. Neither did Augustus give Arius such a role, nor Scipio Panaetius, nor Tiberius Thrasyllus. In these individuals the three statesmen had only observers of their private struggles: even though they might have greatly desired to drag them into the stadium’s dust, they were unable to do so. But this was not the experience of our current emperor’s fathers and the founders of his line [Hadrian, Antoninus Pius, and Marcus Aurelius], whose names are great. They pulled Arrian and [Junius] Rusticus away from their books, refusing to let them be mere pen-and-ink philosophers. They did not let them write about courage and stay at home, or compose legal treatises while avoiding the public domain that is law’s concern, or decide what form of government is best while abstaining from any participation in government. The emperors to whom I am now alluding consequently escorted these men to the general’s tent as well as to the speaker’s platform. In their role as Roman generals, these men passed through the Caspian Gates, drove the Alani out of Armenia, and established boundaries for the Iberians and the Albani. For all these accomplishments, they reaped the fruits of the eponymous consulship, governed the great city [of Rome], and presided over the ancient senate. For the emperors [who thus employed them] knew that it is proper that public office, like the body, be cleansed, and that the greater and more noble the office is, the more cleansing it needs. These emperors understood that opinion was held by the ancient Romans, who saw the learned Cato hold the quaestorship, Brutus the praetorship, Favonius the plebeian tribunate, Varro the office with six axes and Rutilius the consulship. I pass over Priscus, Thrasea, and others of the same sort; writers will sate you with them if you should choose to consult their accounts. Nor was Marcus [Aurelius] himself anything but a philosopher in the purple. The same can be said for Hadrian, Antoninus [Pius], and, of course, for our current ruler Theodosius.
If you should look at his belt and cloak, you will number him with the vast majority of emperors; but if you cast your eyes on his soul and his intellect, you will class him with that famous triad [of philosophical emperors]. For surely he should be placed among those who are similarly minded, not among those who are similarly garbed.