Mainly
from "tribute" -- taxes. The cities they took from the Persians paid
annual tribute to Athens, greatly enriching the city. The Athenian
Greeks also used the conquered areas as colonies, giving land grants to
Greek citizens in the conquered areas, as there was little land left in
Attica (where Athens is) that wasn't already owned.
The tribute was in the form of grain, precious metals, and work products
(leather, pottery, etc.) which Athens usually traded (except for the
grain) to further enrich the city
