ancient and modern settlement on the Saronic Gulf within Attica nomós (department) of Greece. Modern Megara sits on the southern slopes of two hills that served as the acropolises (citadels) of the ancient town.

The early inhabitants were annihilated during the Dorian invasion (c. 1100–c. 1000 BC). In the 8th century BC, Megarian commercial colonies were established on Sicily. Megara also colonized northward and eastward on the Bosporus River and Sea of Marmara at Chalcedon (676) and Byzantium (660), the latter being the most significant in later history. The chief colonies, however, were Astacus and Heraclea in Bithynia in northwestern Asia Minor and a second Heraclea in the Crimea.

The history of Megara after 630 BC is largely that of its losing conflict with its powerful neighbour, Athens, to which it lost the island of Salamís about 570. Forced to accept Athenian defensive assistance after 461, it revolted in 446 and in 432 suffered an Athenian trade embargo throughout its empire. Though its surrounding territory was subjugated by Athens during the Peloponnesian War (431–404 BC), the citadel of Megara itself did not fall. In the 4th century BC Megara recovered some of its prosperity but remained politically insignificant. The city survived the Roman period, but in the 2nd century AD the Greek traveler Pausanias noted that Megarians were the only people whom the emperor Hadrian (117–138) could not make thrive. Although Megara continued as a prominent place for several more centuries, in 1500 it was depopulated by the Venetians. Megara was the birthplace of the Sophist philosopher Eucleides (c. 450–c. 380 BC), who founded the Megarian school of philosophy, which influenced Stoic thought. Modern Megara is a major centre for farming and poultry-raising and has benefited from the rapid industrialization of the coastal areas from Piraeus to Corinth. Pop. (1991 prelim.) 26,562.