Marcus Aurelius Antoninus may have wielded more political power than any other person to have an entry in this encyclopedia. Born into a prominent Roman family in 121 CE, Marcus was adopted in 138 by Emperor Hadrian's heir, Antoninus Pius (at Hadrian's behest), and he succeeded Antoninus as emperor in 161. Marcus's reign is usually judged favorably; indeed, his death in 180 is often thought to end the golden age of the Roman Empire. But it was not all wine and roses: Marcus faced troubles on the frontiers of the empire, a devastating plague, and worst of all, persistent wars that included the first Germanic invasion of Italy in centuries, a harbinger of invasions to come.

By late antiquity, Marcus Aurelius was most famous as a philosopher. This reputation has come to rest on his Greek writings to himself, best known in English as...