  Marcus’ chief philosophical influence was Stoic: in Book I of the Meditations, he records his gratitude to his Stoic teacher and friend Rusticus for giving him Epictetus to read, and in a letter to Fronto written between 145 and 147, he reports reading the 3rd c. BCE Greek Stoic Aristo of Chios and finding intense joy in his teachings, growing ashamed of his own shortcomings, and realizing that he can never again argue opposite sides of the same question, as required by rhetorical practice. The Stoic influence, however, does not prevent Marcus from approvingly quoting Epicurus on ethical matters (as Seneca also had); in addition to Epictetus and Epicurus, Marcus quotes liberally from such figures as Antisthenes, Chrysippus, Democritus, Euripides, Heraclitus, Homer, and Plato. From Book I of the Meditations we also learn that Marcus’ political heroes included republican opponents of kingship: he thanks his adoptive brother Severus not only for exemplifying the love of justice and the vision of a constitution based on equality before the law, but also for the knowledge of Brutus (assassin of Julius Caesar), Cato, Dion (probably of Prusa), (Publius) Thrasea, and Helvidius (i.14). Consonant with this, he warns himself to see to it that he does not become ‘Caesarified’ (that is, act like a dictator, vi.30).