The Classical Age of Greece began around 800 BC and lasted until about 323 BC. This period was marked by the rise of the city-states, such as Athens, Sparta, and Thebes. The city-states were constantly at war with each other, but they also produced some of the greatest minds in history, such as Socrates, Plato, and Aristotle. The Hellenistic period began in 323 BC when Alexander the Great conquered the Persian Empire. Alexander's empire was short-lived, but it had a profound impact on Greek culture. The Hellenistic period ended when Rome conquered Greece in 146 BC.