Alfeiós (Greek: Αλφειός, also romanized as Alpheus, Alpheios, Alfiós) is a river in Peloponnese, Greece. Its source is near Megalopoli in the prefecture Arcadia. It flows along Olympia and empties into the Ionian Sea in the prefecture of Ilia, near Pyrgos. As the longest river in the Peloponnese, at 110 km, the river flows in the prefectures of Arcadia and Ilia. The river begins near Davia in central Arcadia, then it flows between Leontari and Megalopoli and the municipal boundary of Falaisia and Megalopoli in a wooded valley and south of Karytaina and flows north of Andritsina and for about 15 to 20 km with the prefectural boundary with Ilia and Arcadia. It later flows with the provincial boundary of Olympia and Ilia for the rest of the length and the municipal boundary of Olympia and Ali