The main landmark of Athens is the acropolis (412 ft/126 m high), which dominates the city and on which stand the remains of the Parthenon, the propylaea, and the Erechtheum. Occupying the southern part of Athens, the Acropolis is ringed by the other chief landmarks of the ancient city—the Pnyx, where the citizens' assemblies were held; the Areopagus; the Theseum of Hephaesteum, a well-preserved Doric temple of the 5th cent. B.C.; the old Agora and the Roman forum; the temple of Zeus or Olympieum (begun under Pisistratus in the 6th cent. B.C. and completed in the 2d cent. A.D. under Hadrian, whose arch stands nearby); the theatre of Dionysius (the oldest in Greece); and the Odeum of Herodes Atticus.
There are many Roman remains in the "new" quarter, built east of the original city walls by Emperor Hadrian (1st cent. A.D.); there the modern royal palace and gardens also stand. The stadium is E of the Ilissus River. Parts of the ancient city walls are still visible, particularly at the Dipylon, the sacred gate on the road to Eleusis; however, the Long Walls connecting Athens and Piraiévs have almost entirely disappeared. The most noteworthy Byzantine structures are the churches of St. Theodora and of the Holy Apostles, both built in the 12th cent. Athens is the see of an archbishop who presides over the Synod of the Greek Orthodox Church. The city is the seat of the National and Capodistrian Univ. (1837), a polytechnic institute, an academy of sciences, several schools of archaeology, and many museums and libraries. A nuclear research center is nearby, at Aghia Paraskevi.