Who could be citizens of greek city states?

The citizen body comprised those males who were registered with their tribes at birth, or were admitted when necessary to rebuild the city-state after some catastrophe. For a new colony, the male colonists were registered as citizens on foundation. Others were admitted as was necessary to keep the colony going and growing, thereafter the usual registration process applied. There was also in many cities a minimum property qualification. In Athens for example the thetes (non-propertied) were excluded until liberalisation in the 5th Century BCE. In Sparta, the Spartiates (full citizens) did not admit outsiders, and from war attrition their numbers progressively diminished and their power waned accordingly.