An invitation by Darius I to Heraclitus of Ephesus
Expanding on a tradition which is also found in Clement of Alexandria (Strom I 65) which briefly mentions an invitation by Darius I to Heraclitus of Ephesus, Diogenes Laertius produced the imaginary correspondence between the two. The fact that this story is found in both (unrelated) sources shows that there was a story circulating in the 3rd century CE about Darius' admiration for Heraclitus. At the very least, this account fits the probable timeframe of Heraclitus' floruit.
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King Darius, son of Hystaspes, to Heraclitus the wise man of Ephesus, greeting.
You are the author of a treatise On Nature which is hard to understand and hard to interpret. In certain parts, if it be interpreted word for word, it seems to contain a power of speculation on the whole universe and all that goes on within it, which depends upon motion most divine; but for the most part judgement is suspended, so that even those who are the most conversant with literature are at a loss to know what is the right interpretation of your work. Accordingly King Darius, son of Hystaspes, wishes to enjoy your instruction and Greek culture. Come then with all speed to see me at my palace. For the Greeks as a rule are not prone to mark their wise men; nay, they neglect their excellent precepts which make for good hearing and learning. But at my court there is secured for you every privilege and daily conversation of a good and worthy kind, and a life in keeping with your counsels.โ
Heraclitus of Ephesus to King Darius, son of Hystaspes, greeting.
All men upon earth hold aloof from truth and justice, while, by reason of wicked folly, they devote themselves to avarice and thirst for popularity. But I, being forgetful of all wickedness, shunning the general satiety which is closely joined with envy, and because I have a horror of splendour, could not come to Persia, being content with little, when that little is to my mind.
Diogenes Laertius, Lives of Eminent Philosophers, ed. R. D. Hicks (Kansas City Missouri: Harvard University Press, November 1, 2005), 419โ421.