There is a particular passage that I have been trying to dig up an answer to.
2.13: "Nothing is more wretched then a man who traverses everything in a round, and pries into things beneath the earth, as the poet says, and seeks by conjecture what is in the minds of his neighbors, without perceiving that it is sufficient to attend to the demon within him, and to reverence is sincerely."
I've been looking to see if the author is attempting to reference a specific poet, or if he is just saying that poets have commented on his topic throughout history. I'm hoping to find the source material for his poet remark, and dive deeper into his thought process, if there is an actual poet he might have been thinking of.
I originally posted this on /r/askphilosophy but they thought you all might have a better idea.
This quote is probably from Pindar. Its a fragment which, I believe, is today only known indirectly from Plato's Theaetetus (173e):
And all these things the philosopher does not even know that he does not know; for he does not keep aloof from them for the sake of gaining reputation, but really it is only his body that has its place and home in the city; his mind, considering all these things petty and of no account, disdains them and is borne in all directions, as Pindar says, “both below the earth,” and measuring the surface of the earth, and “above the sky,” studying the stars, and investigating the universal nature.
Some (like Harold Fowler) have suggested that it might refer to Pindar's Nemean 10:
And Zeus... said...: “You are my son. But Castor was begotten after your conception by the hero, your mother's husband, who came to her and sowed his mortal seed. But nevertheless I grant you your choice in this. If you wish to escape death and hated old age, and to dwell in Olympus yourself with me and with Athena and Ares of the dark spear, you can have this lot. But if you strive to save your brother, and intend to share everything equally with him, then you may breathe for half the time below the earth, and for half the time in the golden homes of heaven.”
However, from the context I'm doubtful if Marcus is thinking of Nemean. It is probably something lost which we only know from Plato.
Sources: Haines Commentary on Loeb's Marcus Aurelius, Fowler's Commentary on Plato, Svarlien's edition of Pindar's Odes
My "Meditations" translation (Martin Hammond, Penguin Classics 2006) attributes it to Pindar, and the endnote says "fr. 292 Snell".
The Robin Hard translation(Wordsworth 1997) of that passage is somewhat more elucidating.
There is nothing more wretched than one who goes around everything in a circle and, as the poet says, searches into what lies beneath the earth and tries to read the secrets of his neighbour’s soul, yet fails to perceive that it is enough to hold fast on to the guardian-spirit within him and take care of it single-mindedly; and this care is to keep it pure from passion and irresponsibility and discontent with anything that comes from god or man. (M 2.13)
The verse of Pindar quoted here (fr. 292 Snell) is also used in the Theaetetus to describe the philosopher’s mind ‘flying everywhere, as Pindar says, in the depths of the earth, geometrising its surface, and above the heaven, doing astronomy’(173e4—6). Is Marcus criticising Plato’s description of the philosopher? I doubt it very much, for several reasons. First, if 'that one who goes around everything in a circle’ referred to contemplation of the heavens or the universe, it would apply to Marcus himself, who, as observed previously, often writes about seeing the world as a whole and even about following the stars. I thus surmise that his quotation of Pindar here alludes to some kind of curiosity. This is borne out by the fact that Marcus leaves out the second part of Pindar’s verse about the heavens and replaces it with a reference to inquiry into the intentions of others, which he often criticises. His target here is thus useless curiosity about nature or society.
Source: Theoria and schole in Epictetus and Marcus Aurelius. Thomas Benatouil.