(Ἀχαϊ v α, derivation uncertain), a region of Greece, which in the restricted sense occupied the north-western portion of the Peloponnesus, including Corinth and its isthmus (Strabo, 7, p. 438 sq.). By the poets it was often put for the whole of Greece, whence Ἀχαιοί , Acheans, i.e. Greeks. The cities of the narrow slip of country, originally called Achaia, were confederated in an ancient league, which was renewed in B.C. 280 for the purpose of resisting the Macedonians. This league subsequently included several of the other Grecian states, and became the most powerful political body in Greece; and hence it was natural for the Romans to apply the name of Achaia to the Peloponnesus and the south of Greece when they took Corinth and destroyed the league in B. C. 146 (Pausan. 7:16, 10). Under the Romans Greece was divided into two provinces, Macedonia and Achaia, the former of which included Macedonia proper, with Illyricum, Epirus, and Thessaly; and the latter, all that lay southward of the former (Cellar. 1, p. 1170, 1022). It is in this latter acceptation that the name of Achaia is always employed in the New Testament (Acts 18:12; Acts 18:16; Acts 19:21; Romans 15:26; Romans 16:25; 1 Corinthians 16:15; 2 Corinthians 1:1; 2 Corinthians 9:2; 2 Corinthians 11:10; 1 Thessalonians 1:7-8). In the division of the provinces by Augustus between the emperor and the senate in B.C. 27, Achaia was made a senatorial province (Strabo, 17, p. 840), and, as such, was governed by proconsuls (Dion. Cass. 53, p. 704). In A.D. 16 Tiberius changed the two into one imperial province under procurators (Tacit. Annal. 1, 76); but Claudius restored them to the senate and to the proconsular form of government (Suet. I Claud. 25). Hence the exact and minute propriety with which Luke expresses himself in giving the title of proconsul (ἀνθύπατος, "deputy") to Gallio (q.v.), who was appointed to the province (see Smith's Dict. of Class, Ant. s.v.) in the time of Claudius
(Acts 18:12). (See generally Smith's Dict. of Class. Geog. s.v.)