Peoples of the empire: The Medes

History
Herodotus writes that the Medes (Gk. Medoi) were originally called (as rendered in Greek) Arioi, which is almost assuredly related to Old Persian self-designation Ariya, "Aryans."  The Median language is scarcely attested, but appears to have been in the Northwestern Iranian branch and possibly ancestral to Old Azeri.

The historian also says they consisted of six tribes, called (in Latin translation) the Busae (Gk. Busai), Parataceni (Paratakenoi), Struchates (Strukhatai), Arizanti (Arizantoi), Budii (Budioi) and Magi (Magoi).  Magi (sing. magus, Gk. mágos) elsewhere in Greek histories refers to the priests of Media and Persia, and some historians believe that they are one and the same; in other words, that the Median tribe traditionally acted as the Iranians' priests, as the tribe of Levi did among the Israelites.

There is no certainty that the Biblical Magi were Medes, or any sort of Iranians:  By the late Hellenistic period, the term had become generic for priests and scholars from Mesopotamia, the Iranian plateau and the Indian subcontinent.  Its association with occult knowledge, by extension, gave rise to the words "magic" and "mage."  For all that, early portrayals of the Biblical Magi do show them in Iranian (specifically Parthian) clothing, though this may simply be meant to indicate that they came from the same general part of the world.

Media (O.P. Māda) was the first nation the Persians conquered.  It was located in the central Zagros north of Persia.  According to Greek histories, the Medes formed a centralized monarchy centered at Ecbatana (O.P. Hamgmatana, modern Hamadan) between the 7th century BC and 549, when Cyrus overthrew them.  There is as yet no clear archaeological record of such a state.  It likely was more of a tribal confederation, lacking the Achaemenids' political centralization.

The Medes and Persians were at least nominally subject to the Assyrians and often suffered raids or had to pay tribute to them, but between 616 and 605 the Medes allied with the Babylonians and Scythians in overthrowing the Neo-Assyrian empire.  The defeat left the Median confederation and the Babylonian empire as the two great spheres of influence in West Asia, Babylon in most of the Middle East, and Media from the Halys River (modern Kızılırmak) in Turkey to perhaps as far east as Bactria in northern Afghanistan and south as far as Persia.

According to Herodotus, Cyrus was the son of a Median princess and Persian tributary king, thus leading to the famous Delphian quip that Lydia (Cyrus' next conquest) would fall "when a mule sits on the throne of Media."  Medes remained an important part of the early Achaemenid government and military, providing officers such as Mazares and Harpagus, who conquered Asia Minor under Cyrus, and Datis, who (together with Artaphernes) led the first Persian invasion of Greece.

After Alexander conquered the empire, he divided Media into northern and southern satrapies, eventually reinstating the native satrap Atropates (Âtarepâta or Aturpat), who went on to found the kingdom of Atropatene (Aturpatakan), which lent its name to both the Iranian province and the state of Azerbaijan.  The Medes themselves are often held to be ancestral to the Kurds.

Dress, arms and fighting methods
We've already, for all practical purposes, covered Median clothing and arms, which were very similar to those of the Persians, but lacking the elements borrowed from the Elamites, such as the court robe.  Like the Persians, they relied heavily on cavalry and wore the cavalry costume, both in combat and at the royal court.  The Medes in Achaemenid art are attested as carrying the gorytus and akinakes, and are usually identified by their large domed hats.  However, you can also elect to wear a tiara or kidaris, which is the usual headwear for "Persians" in Greek art of the time.