Stoicism was founded in the third century B.C. by Zeno. The name comes from the fact that Zeno taught in the porticos (stoa) of Athens. Stoicism taught that humans are unique in the universe because of their ability to understand and to respond to the reason that controls the universe. Humans cannot control the world; therefore they must try to understand the world and live by the principles that control the world. They encouraged indifference to the environment. One cannot control what happens in one's life. One can, however, control one's reaction and response to it. The stoics emphasized the essential equality of all humans and the concept of the natural rights of all humans.