Where does “Ἐρυθραία” come from?

Ἐρυθραία (Ancient Greek) comes from Ancient Greek Ἐρυθραῖος, from Ancient Greek Ἐρυθραί, from Ancient Greek ἐρυθρός, from Proto-Hellenic *erutʰrós.

Ἐρυθραία (Ancient Greek): Erythraea or Eritrea