At its height, Athens was the center of Greek civilization. Its classical styles of art, architecture, and literature have endured in Western civilization. The Greeks were the first to write and perform plays. Greek thinkers believed that the power of reason could explain all things, a belief that became a basic principle of science. Philosophers such as Socrates, Plato, and Aristotle taught and lectured on several topics. The Greeks also produced the first true historians in Herodotus and Thucydides, and the father of medicine in Hippocrates. Alexander the Great had the goal of combining the best of Greek and Persian cultures into one civilization. After he died, his empire was divided. Although Greek political unity vanished, Greek culture spread and mixed with Middle Eastern cultures to form the Hellenistic civilization.