Achaemenid army in the context of Lydian people

The Ionians (/aɪˈoʊniənz/; Greek: Ἴωνες, Íōnes, singular Ἴων, Íōn) were one of the traditional four major tribes of Ancient Greece, alongside the Dorians, Aeolians, and Achaeans. The Ionian dialect was one of the three major linguistic divisions of the Hellenic world, together with the Dorian and Aeolian dialects.

When referring to populations, "Ionian" defines several groups in Classical Greece. In its narrowest sense, the term referred to the region of Ionia in Asia Minor. In a broader sense, it could be used to describe all speakers of the Ionic dialect, which in addition to those in Ionia proper also included the Greek populations of Euboea, the Cyclades, and many cities founded by Ionian colonists. Finally, in the broadest sense it could be used to describe all those who spoke languages of the East Greek group, which included Attic.

The Lydians (Greek: Λυδοί; known as Sparda to the Achaemenids, Old Persian cuneiform 𐎿𐎱𐎼𐎭) were an Anatolian people living in Lydia, a region in western Anatolia, who spoke the distinctive Lydian language, an Indo-European language of the Anatolian group.

Questions raised regarding their origins, reaching well into the 2nd millennium BC, continue to be debated by language historians and archeologists. A distinct Lydian culture lasted, in all probability, until at least shortly before the Common Era, having been attested the last time among extant records by Strabo in Kibyra in south-west Anatolia around his time (1st century BC).

The Carians (/ˈkɛəriənz/; Ancient Greek: Κᾶρες, Kares, plural of Κάρ, Kar) were the ancient inhabitants of Caria in southwest Anatolia, who spoke the Carian language.

Immortals (Greek: Ἀθάνατοι, Athánatoi), or Persian Immortals, was the name given by the Greek historian Herodotus to a 10,000-strong unit of elite heavy infantry in the Achaemenid army. They served in a dual capacity, operating as an imperial guard and contributing to the ranks of the standing army. The force mainly consisted of Persians, along with Medes and Elamites. Essential questions regarding the unit's history and organization remain unanswered due to the lack of authoritative sources.