The Greek polis was not the first form of city-state to emerge. The earliest states in Sumer were also city-states, as were many of the small Mycenaean kingdoms. What differentiated the new Greek model from older city-states is the fact that the polis was more than a political institution; it was a community of citizens with their own customs and laws. With one exception, the poleis that emerged after 800 did not have kings but instead were self-governing. The physical, religious, and political forms of the polis varied from place to place, but everywhere the polis was relatively small, reflecting the fragmented geography of Greece. The very smallness of the polis enabled Greeks to see how they fit individually into the overall system — and how the individual parts made up the social whole. This notion of community was fundamental to the polis and was the very badge of Greekness.

Poleis developed from Dark Age towns. When fully developed, each polis normally shared a surprisingly large number of features with other poleis. Physically a polis was a society of people who lived in a city (asty) and cultivated the surrounding countryside (chora). The countryside was essential to the economy of the polis and provided food to sustain the entire population. By the fifth century B.C.E., the city was generally surrounded by a wall. The city contained a point, usually elevated, called the acropolis, and a public square or marketplace called the agora (ah-guh-RAH). On the acropolis, people built temples, altars, public monuments, and various dedications to the gods of the polis. The agora was the political center of the polis. In the agora were shops, public buildings, and courts.

All poleis, with one exception, did not have standing armies. Instead they relied on their citizens for protection. Wealthy aristocrats often served as cavalry. The backbone of the army, however, was the heavily armed infantry, or hoplites, ordinary citizens rather than members of the elite.