<P> The site on which Athens stands was first inhabited in the Neolithic period, perhaps as a defensible settlement on top of the Acropolis (' high city'), around the end of the fourth millennium BC or a little later . The Acropolis is a natural defensive position which commands the surrounding plains . The settlement was about 20 km (12 mi) inland from the Saronic Gulf, in the centre of the Cephisian Plain, a fertile valley surrounded by rivers . To the east lies Mount Hymettus, to the north Mount Pentelicus . </P> <P> Ancient Athens, in the first millennium BC, occupied a very small area compared to the sprawling metropolis of modern Greece . The ancient walled city encompassed an area measuring about 2 km (1 mi) from east to west and slightly less than that from north to south, although at its peak the ancient city had suburbs extending well beyond these walls . The Acropolis was situated just south of the centre of this walled area . </P> <P> The Agora, the commercial and social centre of the city, lay about 400 m (1,312 ft) north of the Acropolis, in what is now the Monastiraki district . The hill of the Pnyx, where the Athenian Assembly met, lay at the western end of the city . The Eridanus (Ηριδανός) river flowed through the city . </P> <P> One of the most important religious sites in ancient Athens was the Temple of Athena, known today as the Parthenon, which stood on top of the Acropolis, where its evocative ruins still stand . Two other major religious sites, the Temple of Hephaestus (which is still largely intact) and the Temple of Olympian Zeus or Olympeion (once the largest temple in mainland Greece but now in ruins) also lay within the city walls . </P>

In athens the most important occupation of an athenian was as a