Achaia was the name of the Roman province that covered mainland southern Greece and the Peloponnese, with Corinth as its main city and the seat of Roman government.
The apostle Paul arrived there during his second missionary journey and stayed about a year and a half teaching the word of God (Acts 18:11).
In Corinth, the capital of Achaia, Jews brought Paul before the tribunal of the Roman proconsul Gallio, accusing him of teaching worship contrary to the law. Gallio refused to judge the case, considering it an internal dispute over the Jewish religion.
After Paul, the preacher Apollos went to Achaia and greatly helped those who had already believed, debating with the Jews in public. The household of Stephanas was remembered as the first fruit of faith in the region.
The churches of Achaia, alongside those of Macedonia, contributed an offering for the poor Christians in Jerusalem, a gesture Paul cites as an example of generosity.
Paul addressed two of his letters to this region: the first epistle to the Corinthians and the second, addressed explicitly to all the saints throughout Achaia.
