There's heaps and heaps of scholarship based on the Athenian tribute lists; none of those lists suggest that the poleis Athens was taxing were particularly large or wealthy or well-armed for that matter (which is why Athens started collecting money).
100,000 in the entire hinterland with the slaves included AND all the citizens in posts abroad...maybe that could have been Athens. 20 million is just completely off the usual population estimates to a dramatic degree.
Not really heaps they are selected few and Russel Meiggs wrote his History of the Athenian Empire based AND on those lists.;The APA(American Philosophical Association) reports from the lists in an extract that Cleon composed along with leading Athenians a list at 424/5 of 400 cities due to pay tribute.Many don't realize that Athens had a lot of its members in the west.That number of cities were capable of having the above mentioned population easily;however,the original cities were 178 and the list kept growing.