anciently a small district in the north of Peloponnesus, running westward along the bay of Corinth, and bounded on the west by the Ionian Sea, on the south by Elis and Arcadia, and on the east by Sicyonia: inhabitants, the Achæans, properly so called; its metropolis, Patra. It is now called Romania Alta, in the Morea.

Achaia was also taken for all those countries that joined in the Achæan league, reduced by the Romans to a province. Likewise for Peloponnesus.

**ACHÆI PREBUTERI**, or the Presbyters of Achaia, were those who were present at the martyrdom of St Andrew the Apostle, A.D. 59; and are said to have written an epistle in relation to it. Bellarmin, and several other eminent writers in the church of Rome, allow it to be genuine; while Du Pin, and some others, expressly reject it.