http://agathe.gr/democracy/the_athenian_army.html
The Athenian Army From the very beginning, the Athenians were compelled to fight for their new democracy. Their dramatic victories over the Boiotians and Chalkidians in 506 B.C. led many to attribute Athenian ... Public armor was most likely kept on hand for the arming of irregulars, thetes, and perhaps even slaves, at the time of mobilization, whereas Athenians on the official hoplite register were legally responsible for procuring their own military equipment.