Stoicism, the most influential philosophy of the Roman Empire, offers refreshingly modern ways to strengthen our inner character in the face of an unpredictable world. Widely recognized as the most talented and humane writer of the Stoic tradition, Seneca teaches us to live with freedom and purpose. His most enduring work, over a hundred "Letters from a Stoic" written to a close friend, explains how to handle adversity; overcome grief, anxiety,...