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, ... The earliest references to a monument of the Eponymous Heroes came from the comic poet Aristophanes in the 420's B.C., but the foundations of the monument that have been excavated belong to the years around 330 B.C., nearly a century later. 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. ... Aerial view showing the foundations of the Monument of the Eponymous Heroes (center).