from
Easton's 1897 Bible Dictionary
Achaia
the name originally of a narrow strip of territory in Greece, on
the north-west of the Peloponnesus. Subsequently it was applied
by the Romans to the whole Peloponnesus, now called the Morea,
and the south of Greece. It was then one of the two provinces
(Macedonia being the other) into which they divided the country
when it fell under their dominion. It is in this latter enlarged
meaning that the name is always used in the New Testament (Acts
18:12, 27; 19:21; Rom. 15: 26; 16:5, etc.). It was at the time
when Luke wrote the Acts of the Apostles under the proconsular
form of government; hence the appropriate title given to Gallio
as the "deputy," i.e., proconsul, of Achaia (Acts 18:12).