Why was the size of the polis important?

Like a state, each polis was also involved in international affairs, both with other poleis and non-Greek states in the areas of trade, political alliances and wars. ... The biggest was Sparta, although with some 8,500 km² of territory, this was exceptionally large and most poleis were small in size.

A city-state, or polis, was the community structure of ancient Greece. Each city-state was organized with an urban center and the surrounding countryside. ... The majority of a polis's population lived in the city, as it was the center of trade, commerce, culture, and political activity.