Achaia
Archimandrite Nikifor’s Biblical Encyclopedia
(Acts 18:12; Rom. 16:5; 1 Cor. 11:10 [as given]) — this name originally designated a small state in the northern part of the Greek Peloponnese, now called the Morea. In later times, and under Roman rule, this name was applied to the whole Peloponnese and the part of the country north of it as far as Thessaly itself. For this reason, as D. Howson notes, its boundaries corresponded to the boundaries of present-day Greece. The whole region now called Greece was, in New Testament times, divided into Achaia and Macedonia, with the nearby islands.
The first governors of Roman Achaia were proconsuls. Tiberius appointed procurators over it, but Claudius again replaced them with proconsuls. Gallio, mentioned in chapter 18 (verse 12) of the Book of Acts of the Holy Apostles, was one of these proconsuls; Corinth was the capital of Achaia. In the New Testament this name is always used in the broadest sense. The Apostle Paul preached the Gospel here on his first journey, and partly on his third (Acts 17:15 and elsewhere).