Originally a state of Greece situated in the northern part of the Peloponnesus (now the Morea), and comprehending Corinth and its isthmus.
After Greece had been conquered by the Romans, the emperor Augustus Caesar divided that country with the adjacent regions into two provinces, Macedonia and Achaia. The latter comprehended the whole of the Peloponnesus, with continental Greece south of Illyricum, Epirus, and Thessaly.
Corinth was the capital, and was the residence of the proconsul by whom the province was ruled. It is in the second or comprehensive sense that the word Achaia is used in the New Testament (Acts 18:12, 27; 19:21; Rom. 15:26; 2 Cor. 1:1; 9:2; 1 Thess. 1:7, 8).