Early in the 4th century BC the 12 cities of Achaea formed the Achaean League, a military alliance. In Hellenistic times, the League admitted non-Achaean allies and became the chief political power in Greece. It went over to Rome in 198 BC but was dissolved by the Romans in 146 BC, after which it was annexed to the Roman province of Macedonia. In 27 BC it became the centre of the Roman senatorial province of Achaea, which included all of Greece south of Thessaly. After various invasions and dismemberments in the Middle Ages, Achaea was conquered by the Turks in 1460. It was in the monastery of Ayía Lavra near Kalávrita in this province that the standard of the Greek Revolution was raised in 1821. Achaea was liberated from the Turks in 1828. (Encyclopædia Britannica Online.)
The league or confederation of a number of towns on the northwest coast of Peloponnesus. In speaking of it we must distinguish between two periods. The former, though formed for mutual protection, was mainly of a religious character, whereas the latter was a political confederation to protect the towns against the domination of Macedonia.
(1) The Earlier League. When the Heraclidae took possession of Peloponnesus, a portion of the Achaeans, under Tisamenos, turned northwards and took possession of the northern coast of the peninsula, which was called Aigialos: the Ionians, who had hitherto occupied that country, sought refuge in Attica and on the west coast of Asia Minor. The country thus occupied by the Achaeans, from whom it derived its name of Achaia, contained twelve towns which had been leagued together even in the time of their Ionian inhabitants. They were governed by the descendants of Tisamenus, until, after the death of King Ogyges, they abolished the kingly rule and established democratic institutions. The time when this happened is not known. In the time of Herodotus (i. 145) the twelve towns of which the league consisted were: Pellene, Aegeira, Aegae, Bura, Helicé, Aegion, Rhypes, Patrae, Pharae, Olenos, Dymé, and Tritaea. After the time of Herodotus, Rhypes and Aegae disappear from the number of the confederate towns, as they had decayed and become deserted (Paus. vii.23.25; Strab.viii. p. 387), and Leontion and Cerynea stepped into their place (Polyb. ii. 41). Helicé appears to have been their common place of meeting; but this town, together with Bura, was swallowed up by the sea during an earthquake in B.C. 373, whereupon Aegion was chosen as the place of meeting for the confederates (Strab. viii. p. 384). Of the constitution of this league very little is known; but it is clear that the bond which united the different towns was very loose, and less a political than a religious one. The looseness of the connection among the towns in a political point of view is evident from the fact that some of them acted occasionally quite independent of the rest (Thuc.ii. 9). The confederation generally kept aloof from the troubles of other parts of Greece, on which accordingly it exercised no particular influence down to the time when the league was broken up by the Macedonians. But they were nevertheless highly respected by the other Greek states on account of their honesty, sincerity, and wise moderation. Hence after the battle of Leuctra they were chosen to arbitrate between the Thebans and Lacedaemonians (Polyb. ii. 39). Demetrius, Cassander, and Antigonus Gonatas placed garrisons in some of their towns, while in others they favoured the rising of tyrants. The towns were thus separated from one another, and the whole confederation was gradually destroyed.
(2) The Later League. The ancient confederacy had thus ceased to exist for some time when events took place which in some towns roused the ancient spirit of independence. When in B.C. 281 Antigonus Gonatas attempted to drive Ptolemaeus Ceraunus from the throne of Macedonia, the Achaeans availed themselves of the opportunity of shaking off the Macedonian yoke, and renewing the old confederation. The object, however, was no longer a common worship, but a real political union among the towns. The places which first shook off the yoke of the oppressors were Dymé and Patrae, and the alliance concluded between them was speedily joined by the towns of Tritaea and Pharae (Polyb. ii. 41). One town after another expelled the Macedonian garrisons and tyrants; and when in B.C. 275, Aegion, the head of the ancient league, followed the example of the other towns, the foundation of the new confederation was complete, and the main principles of its constitution were settled, though afterwards many changes and modifications were introduced. The fundamental laws were that henceforth the confederacy should form one inseparable state; that every town which should join it should have equal rights with the others; and that all members in regard to foreign countries should be regarded as dependent, and be bound in every respect to obey the federal government and those officers who were intrusted with the executive (Polyb. ii. 37 foll.). No town, therefore, was allowed to treat with any foreign power without the sanction of the others. Aegion, for religious reasons, was appointed the seat of the government. At Aegion, therefore, the citizens of the various towns met at stated and regular times [p. 9] to deliberate upon the common affairs of the confederation, and if necessary upon those of any separate town or even of individuals, and to elect the officers of the league. After having thus established a firm union among themselves, the Achaeans zealously exerted themselves in delivering other towns also from their tyrants and oppressors. The league, however, did not acquire any great strength until B.C. 251, when Aratus united Sicyon, his native place, with it, and some years later also gained Corinth for it. Megara, Troezen, and Epidaurus soon followed their example. Afterwards Aratus prevailed upon all the more important towns of Peloponnesus to join the confederacy, and Megalopolis, Argos, Hermioné, Phlius, and others were added to it. In a short time the league thus reached its highest power, for it embraced Athens, Aegina, Salamis, and the whole of Peloponnesus, with the exception of Sparta, Tegea, Orchomenus, Mantinea, and Elis. Greece seemed to revive, and promised to become stronger and more united than ever, but it soon showed that its new power was employed only in self-destruction and its own ruin. The Achaean League might at one time have become a great power, and might have united at least the whole of Peloponnesus into one State; but the original objects of the league were in the course of time so far forgotten that it sought the protection of those against whom it had been formed; and the perpetual discord among its members, the hostility of Sparta, the intrigues of the Romans, and the folly and rashness of the last strategy brought about not only the dissolution and destruction of the confederacy, but the political annihilation of the whole of Greece in the year B.C. 146. (Cf. Schorn, Gesch. Griechenlands von der Entstehung des aetol. u. achaeischen Bundes, p. 49 foll. and p. 60 foll.; Drumann, Ideen zur Gesch. des Verfalls der griech. Staaten; Thirlwall, Hist. of Greece, vol. viii p. 86 foll.; Hertzberg, Gesch. Griechenlands unter den Römern, vol. i. [Halle, 1875].)
(Harpers Dictionary of Classical Antiquities, 1898)
Historic region of Greece on the north coast of the Peloponnese, south of the Gulf of Corinth. In ancient times it was bounded on the west by Elis (modern Ilía), on the south by Mount Erymanthus and Arcadia, and on the east by Sicyon (modern Sikión). The hilly coastal region almost corresponds to the modern nomós of Akhai¨´a, whose administrative capital is Pátrai, although the eastern boundary now falls west of Mount Kyllene (Killíni Óros). The highway and railway from Athens to Pátrai follow the north coast of the Peloponnese.