Seneca delighted much in a work of Sextius, the title of which he does not give, but which he praises, as written with great power:
Ye Gods, what strength and spirit one finds in him! This is not the case with all philosophers; there are some men of illustrious name whose writings are sapless. They lay down rules, they argue, and they quibble; they do not infuse spirit simply because they have no spirit. But when you come to read Sextius you will say: "He is alive; he is strong; he is free; he is more than a man; he fills me with a mighty confidence before I close his book." I shall acknowledge to you the state of mind I am in when I read his works: I want to challenge every hazard; I want to cry: "Why keep me waiting, Fortune? Enter the lists! Behold, I am ready for you!
Seneca describes Sextius as a Stoic but mentions that Sextius himself denied it. From other Epistles of Seneca we learn that Sextius, though born of an illustrious family, had declined the dignity of Senator when offered him by Julius Caesar; that he subjected himself to a scrupulous self-examination at the close of each day; and that he abstained from animal food, though for different reasons than those ascribed to Pythagoras:
Sextius believed that man had enough sustenance without resorting to blood, and that a habit of cruelty is formed whenever butchery is practised for pleasure.
It appears that Sextius attempted to found a school of philosophy combining some features of the Pythagoreans with others of the Stoics; and which was consequently classed sometimes with one, and sometimes with the other of those sects. Seneca writes (c. 65 AD) that the school was extinct.
A Xystus Pythagoricus philosophus is recorded in Jerome's version of the Chronicon of Eusebius. He is also mentioned by Plutarch, and by the elder Pliny. It has sometimes been suggested that the extant Sentences of Sextus were (in their original form) written by Sextius.