http://agathe.gr/democracy/the_ten_new_tribes.html
The Ten New Tribes Kleisthenes instituted a crucial reform, the reorganization of the citizenry into new administrative units called phylai (tribes). In his attempt to break up the aristocratic power structure, ... Located immediately east of the Metroon, the monument consisted of a base over 16 meters long that supported bronze statues of the ten heroes, with tripods at either end, presumably to reflect the role of Apollo's oracle at Delphi in their selection.