Aetius (c. 150 B.C.E.) is the alleged author of a doxographical work, the Placita philosophorum , which mainly discusses pre-Socratic philosophers and their doctrines. The extant Greek version is attributed to Plutarch (fl. second century C.E.) and is based on a lost doxographical work, a summary of Theophrastus's "Doctrines of the physicians." The text is the most important source on Greek philosophers before and after Socrates, including the Stoics. It discusses doctrines on the principles of existence, the world, meteorology, the earth, the soul, and the