Marcus Aurelius (26 April 121 - 17 March 180 AD) was Roman Emperor from 161 to 180. He ruled with Lucius Verus as co-emperor from 161 until Verus' death in 169. He was the last of the Five Good Emperors, and is also considered one of the most important Stoic philosophers.During his reign, the Empire defeated a revitalized Parthian Empire in the East; Aurelius' general Avidius Cassius sacked the capital Ctesiphon in 164. In central Europe, Aurelius fought the Marcomanni, Quadi, and Sarmatians with success during the Marcomannic Wars, with the threat of the Germanic tribes beginning to represent a troubling reality for the Empire. A revolt in the East led by Avidius Cassius failed to gain momentum and was suppressed immediately.Marcus Aurelius' Stoic tome Meditations, written in Greek while on campaign between 170 and 180, is still revered as a literary monument to a philosophy of service and duty, describing how to find and preserve equanimity in the midst of conflict by following nature as a source of guidance and inspiration.The major sources for the life and rule of Marcus Aurelius are patchy and frequently unreliable. The most important group of sources, the biographies contained in the Historia Augusta, claim to be written by a group of authors at the turn of the 4th century, but are in fact written by a single author (referred to here as "the biographer") from the later 4th century (c. 395).The later biographies and the biographies of subordinate emperors and usurpers are a tissue of lies and fiction, but the earlier biographies, derived primarily from now-lost earlier sources (Marius Maximus or Ignotus), are much more accurate.[4] For Marcus' life and rule, the biographies of Hadrian, Antoninus Pius, Marcus and Lucius Verus are largely reliable, but those of Aelius Verus and Avidius Cassius are full of fiction.A body of correspondence between Marcus' tutor Fronto and various Antonine officials survives in a series of patchy manuscripts, covering the period from c. 138 to 166. Marcus' own Meditations offer a window on his inner life, but are largely undateable, and make few specific references to worldly affairs. The main narrative source for the period is Cassius Dio, a Greek senator from Bithynian Nicaea who wrote a history of Rome from its founding to 229 in eighty books. Dio is vital for the military history of the period, but his senatorial prejudices and strong opposition to imperial expansion obscure his perspective.Some other literary sources provide specific detail: the writings of the physician Galen on the habits of the Antonine elite, the orations of Aelius Aristides on the temper of the times, and the constitutions preserved in the Digest and Codex Justinianus on Marcus' legal work. Inscriptions and coin finds supplement the literary sources.