"The 100 best nonfiction books: No 68 - Narrative of the Life of Frederick Douglass, an American Slave by Frederick Douglass (1845)" by Robert McCrum, www.theguardian.com. May 22, 2017.
Marcus Aurelius, Epictetus, Lucius Annaeus Seneca (2015). “Stoic Six Pack: Meditations of Marcus Aurelius The Golden Sayings Fragments and Discourses of Epictetus Letters from a Stoic and The Enchiridion”, p.499, Lulu.com