Little to none of his work has survived intact, so what we know is mostly through other people. IIRC, a lot comes from Seneca and Marcus Aurelius's auto biograp

Little to none of his work has survived intact, so what we know is mostly through other people. IIRC, a lot comes from Seneca and Marcus Aurelius's auto biography "meditations". Searching around on Seneca, his letters on the topic have been collected in a book "Letters from a Stoic"