Aristotle, Metaphysics (335 B.C.E.)—This work contains an examination of earlier philosophers as well as Aristotle's own account of how the universe was created.

Diogenes Laertius, Lives of the Eminent Philosophers (early third century C.E.)—This collection of biographies of the Greek philosophers is one of the major sources for modern knowledge of ancient philosophy.

Epictetus, Discourses (100 C.E.)—This record of the exchanges between the Stoic philosopher Epictetus and his students is one of the few sources available on Stoicism.

Marcus Aurelius, The Meditations (c. 175 C.E.)—This last great statement of Stoic philosophy was written by the emperor Marcus Aurelius as he campaigned on the German frontier against the Quadi and the Marcomanni in the 170s.

Plato, The Republic (c. 429–347 B.C.E.)—Plato's most famous work is one of the best surviving studies of ancient Greek government...