Ancient Greece developed many independent city-states due to its mountainous terrain. The Greeks traded extensively by sea, spreading their culture and developing new ideas. Athens emerged as a cultural and intellectual center during the Golden Age, when philosophers like Socrates, Plato, and Aristotle expanded knowledge in many fields. However, constant warfare weakened the Greek city-states, allowing Macedonia and its king Alexander the Great to conquer much of the known world and spread Hellenistic culture before his early death. This period saw advances in science, mathematics, and new Greek cities and trade routes.