The Achaei were an ancient people of Scythia

Scythia

In antiquity, Scythian or Scyths were terms used by the Greeks to refer to certain Iranian groups of horse-riding nomadic pastoralists who dwelt on the Pontic-Caspian steppe...

, mentioned by Strabo

Strabo

Strabo, also written Strabon was a Greek historian, geographer and philosopher.-Life:Strabo was born to an affluent family from Amaseia in Pontus , a city which he said was situated the approximate equivalent of 75 km from the Black Sea...

 (11.2, together with the Zygoi, Heniochi, and Cercetae

Cercetae

The Cercetae are an ancient people of Scythia mentioned by Strabo and Pliny the Elder .Pliny places them beyond the Amazons and the Hyperboreans, together with the Cimmerii, Cissianti, Achaei, Georgili, Moschi, Phoristae and Rimphaces....

 and Macropogones) and by Pliny (4.26.2). Pliny mentions a Portus Achaeorum at the mouths of the Danube

Danube

The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....

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The name has been interpreted to mean "river dwellers", from an Indo-European word for "water" (Latin aqua, Old High German aha; Wissowa, Pauly's Real-Encyclopadie s. v. Achaei)