The earliest settlement in the region predates the city of Phlius itself. According to Strabo, the ancient capital was Araethyrea, perched on Mount Celosse — a city mentioned by Homer. The inhabitants later abandoned it and built Phlius some 30 stadia away. Pausanias offers a slightly different account: the original settlement was called Arantia after its mythological founder Aras, then renamed Araethyrea after a daughter of Aras, then finally Phlius after Phlias, a son of Ceisus and grandson of the hero Temenus. Another tradition tied the name to Dionysus and a figure called Chthonophyle — appropriate for a wine-growing territory. Dorian settlers eventually conquered the region, and some of the original inhabitants left for Samos. Among the settlers at Samos, ancient sources record, was a man named Hippasus, from whom Pythagoras traced his own descent. The city never grew large. Estimates of its citizen population in the classical period hover around 5,000 adult males — modest even by Peloponnesian standards. But what it lacked in size it compensated for in stubbornness.

Phlius occupies a curiously prominent role in the narrative of Spartan power politics, given its small size. Geographically close to Argos — a rival that frequently sought to dominate the region — Phlius chose Sparta as its protector and stuck with that choice through decades of pressure and occasional violence. It sent 200 soldiers to Thermopylae and 1,000 to Plataea, proportionally significant contributions from a city of its scale. During the whole of the Peloponnesian War it remained faithful to Sparta and hostile to Argos, a stance that made it both a reliable ally and a frequent target. The political troubles deepened in the 4th century BC. Factional strife between democratic and oligarchic factions drove some citizens into exile, who then appealed to Sparta for intervention. In 380 BC, Agesilaus arrived with an army and besieged the city. Phlius held out for a year and eight months before surrendering through sheer exhaustion of provisions in 379 BC. Agesilaus then installed a council of 100 with powers of life and death. It was an occupation dressed as a constitution.

For all its military entanglements, Phlius is remembered in the history of literature for a quieter achievement. Pratinas of Phlius, who competed in Athens against Aeschylus himself, is credited as the inventor of the satyr play — the ribald, goat-chorus drama that rounded out the tragic trilogy at the Athenian festivals and gave us, eventually, the word 'satire.' His son Aristias was buried in the agora of Phlius, and both men were celebrated figures in the city's memory. Perhaps equally surprising is Phlius's connection to Plato. Axiothea of Phlius, who reportedly read Plato's Republic and travelled to Athens to study under him directly, was one of the very few women known to have done so. She is said to have dressed as a man to gain admission. Whether that detail is true or apocryphal, her presence in Plato's school — coming from this small upland city — is a remarkable footnote to the history of ancient education.

When Pausanias visited in the 2nd century AD, he found a city with a fully developed sacred landscape. On the acropolis stood a temple of Hebe — also called Ganymeda — set within a cypress grove that enjoyed the right of asylum: anyone who reached it could not be seized. There was also a temple of Demeter on the heights. Descending from the citadel, one passed a temple of Asclepius, and below that a theatre. The agora held other public buildings and the tomb of Aristias. It reads like a modest, well-ordered provincial city that had survived its turbulent past and arrived, if not at greatness, then at a comfortable civic dignity. The site of ancient Phlius lies near the modern town of Nemea. The upland valley is still recognisably the same enclosed, mountain-ringed plain that the ancients described — still growing grapes, still surrounded by the same limestone ridges, still finding its own quiet way through time.