They were some of the largest cities of the Greek world. Herodotus tells us that Cyrene (in modern Libya) could field 6000 hoplites in the mid-6th century BC, which means it would be outmatched only by the biggest communities of the Greek mainland. In the Classical period, Syracuse (in Sicily) was the second largest Greek city after Athens; by the later 4th century BC it may have been the largest altogether.

The main thing about Greek "colonisation" is that it was nothing like modern colonisation, where a wealthy and powerful centre extracts wealth from a relatively underdeveloped periphery. The Greeks simply founded new and autonomous communities overseas in areas that seemed fertile or strategically placed. There was no functional difference between these settlements and the city-states of the homeland. At most, there was a loose connection of patronage between a colony and its mother city (metropolis), meaning that each could rely on the other's support in war, but this was only invoked when it was expedient.