The Pnyx is a small, rocky hill platform with steps carved on its slope. It was the meeting place of one of the world's earliest known democratic gatherings, the Athenian assembly, and the flat stone platform in its base was the bema, or the speakers' platform. As such, the Pnyx is the material embodiment of the principle of isegoria, "equal speech", the equal right of every citizen to debate matters of policy. The other two principles of democracy were isonomia, equality under the law, and isopoliteia, equality of vote and equal opportunity to assume political office. The right of isegoria was expressed by the presiding officer of the Pnyx assembly, who formally opened each debate with the open invitation "Tis agoreyein bouletai?" ("Who wishes to speak?"). with a large flat platform of eroded stone The Pnyx was used for popular assemblies in Athens as early as 507 BC, when the reforms of Cleisthenes transferred political power to the citizens. The Pnyx, looks down on the ancient Agora, which was the commercial and social centre of the city. At this site all the great political struggles of Athens of the "Golden Age" were fought out. Pericles, Aristides and Alcibiades spoke here, within sight of the Parthenon.