Greek city-states, known as poleis, were independent communities that developed in ancient Greece. Each city-state had its own government, laws, and customs, often centered around a fortified city and its surrounding territory. The most famous city-states included Athens, known for its democratic system, and Sparta, recognized for its military discipline. These city-states often competed with one another for resources and power, leading to conflicts such as the Peloponnesian War. Despite their rivalries, they shared a common language and culture, which included religion, art, and philosophy, contributing to the rich heritage of ancient Greek civilization.