Achaea (/əˈkiːə/) or Achaia (/əˈkaɪə/), sometimes transliterated from Greek as Akhaia[2] (Αχαΐα, Akhaḯa [axaˈia]), is one of the regional units of Greece.

Achaea is bordered by Elis to the west and southwest, Arcadia to the south, and Corinthia to the east and southeast.

Its main rivers ordered from west to east are the Larissos, Tytheus, Peiros, Charadros, Selinountas and Vouraikos.

The Achaean League was a Hellenistic-era confederation of city states in Achaea, founded in 280/281 BC.

[citation needed] In AD 51/52, Lucius Junius Gallio Annaeanus was proconsul of Achaea,[4] and is portrayed (under the name "Gallio") in the book of the Acts of the Apostles, in the Bible, as presiding over the trial of the Apostle Paul in Corinth (Acts 18:12–17).

The coastal cities remained largely under Byzantine control, and a Siege of Patras in 805/807 failed.

By the end of the 9th century, the whole peninsula was firmly under Byzantine control again, forming the Theme of the Peloponnese.

As a part of the Morean War, the Republic of Venice captured Achaea in 1687 and held it until 1715, when the Ottomans recaptured the Peloponnese.

Achaea saw an influx of refugees that arrived from Asia Minor during the Greco Turkish War of 1919-1922.

Tens of thousands were relocated to their camps in the suburbs of Patras and a few villages mainly within the coastline.

A narrow gauge railway track runs for 30 km, mainly as a tourist attraction.

The main highways are: Intercity bus transport is provided by KTEL Achaias.

There are two skiing resorts, one on the Panachaicus west of the mountain top (elevation around 1700 m) east of Patras, it will be Nafpaktos's closest because of the new bridge (mid-2004) and the other on Aroania, sometimes still called Chelmos, near Kalavrita.