The ancient Greek world was made up of small, independent regions known as city-states, or poleis. Each city-state had its own government, laws, and customs, making them unique. Some of the most famous city-states were Athens, known for its democracy and culture, and Sparta, famous for its military strength and discipline. These city-states often competed with each other for power and resources, leading to conflicts like the Peloponnesian War. Despite their rivalries, they shared a common language and religion, which helped unite them during times of crisis, such as the Persian Wars.