Stoicism is a philosophical movement and practical guide to living, emphasizing daily self-discipline and moral improvement, which originated in the Hellenistic period of ancient Greece and proliferated well into the Roman Imperial period. The ancient Stoics believed that the universe operated according to reason, or logos, providing a unified account of the world, constructed from ideals of rational discourse, monistic physics, and naturalistic ethics. These ideals constitute virtue, which is necessary for the Stoic goal of 'living a well-reasoned life'.