Zeno of Citium (c. 335-263 BC) is generally credited with founding Stoic philosophy. Stoicism’s name derives from the Greek word stoa, which denotes the porch within the Athenian Agora where followers of the philosophy gathered to lecture and discuss. Its three main branches were: logic, the study of rational discourse; physics, the study of the cosmic order; and ethics, the study of proper human behavior. Stoicism became one of the leading philosophical schools in the Roman Empire, with Marcus’s own primary interest being the study of ethics.

At the time Marcus wrote down his Meditations, Stoicism had codified a few key concepts. First, happiness derives from living virtuously. Good health and wealth are morally indifferent and not necessary preconditions for happiness. Second, how humans respond to events and what they desire flow from what they believe is valuable and worth pursuing, which Stoics would say may be morally mistaken beliefs and desires. For example, fearing death and wanting to live longer result from having mistaken beliefs about life and death. Third, humans are naturally disposed to benefit each other. When properly cultivated, this natural disposition leads to humans regarding each other as parts of a larger Whole.