or came to be seen as detrimental to Athens. There was a rule that citizens aged over 50 had a right to be heard first. Democratic government at Athens was suspended in 411 BC and again in 404 BC with the assumption of power by oligarchies during crises in the Peloponnesian War. The Spartans and their allies in Athens installed a dictatorship, called the Thirty Tyrants, but in 403 BC the democrats seized power again and the meetings at the Pnyx resumed. Athens lost its independence to Philip II of Macedon after the battle of Chaeronea in 338 BC; but they continued to run their internal affairs democratically until the coup by Demetrius of Phaleron in 322 BC. After his fall, the Athenians continued to run their internal affairs according to democratic forms for centuries. Excavations Excavations at the site were begun in 1910 by the Greek Archaeological Society and definitely confirmed the site as the Pnyx. Large-scale excavations were conducted at various times between 1930 and 1937 by Homer Thompson, in collaboration first with K. Kourouniotes and later with Robert Scranton. These excavations discovered the foundations of the important buildings at the Pnyx, although nothing else remains of them. These included the two large stoas, erected between 330 and 326 BC, the Altar of Zeus Agoraios, erected at the same time, but removed during the reign of Augustus (first century BC), and the Sanctuary of Zeus Hypsistos. Most of these buildings were erected after the Pnyx had lost its real significance. West to the Altar of Zeus are the foundations of Meton's heliotropion, the oldest known astronomical observatory, where he performed several of his measurements that led to the calculations involving the eponymous 19-year Metonic cycle which he introduced in 432 BC into the lunisolar Attic calendar, a calendar that appears in the Antikythera Mechanism. Today the site of the Pnyx is under the control of the Ephorate of Prehistorical and Classical Antiquities of the Greek Ministry of Culture. The surrounding parkland is fenced, but can be visited free of charge at any time. References External links Ancient Greek buildings and structures in Athens Athenian democracy Hills of Athens Landmarks in Athens