Peoples of the empire: The Ethiopians

Geographical definition 
In ancient Greek geography, Aithiopia (literally "land of Aithiops" but commonly interpreted "land of burned faces") refers broadly to all of Africa south of Egypt and "Libya" (all the desertified regions of North Africa).  However, the Greeks apparently weren't aware of just how vast an area this is.

The "Ethiopians" in the Persian empire were mainly from Kush (Kaš, or in Persian Kušâ-), which consisted of the Nile Valley south of Elephantine to some ways south of the confluence of the White and Blue Nile at modern Khartoum.  Thus this article would better be called "The Kushites," but in keeping with the lists presented by Herodotus, we'll stick with "Ethiopians" at least for the title.  Today histories often refer to the ancient land as Nubia, named after the Nuba people who settled there in late antiquity.

Herodotus also refers to "Ethiopians of Asia" or "of the East," who are armed like Indians, and have straight hair as distinguished from Ethiopians of Africa.  As they are presumably also dark-skinned, one is tempted to identify them with South Indians like the Tamils, but circumstantial geographic references seem to place them north of India.  I can find too little information to give them their own article.

History
While archaeology and Egyptian annals indicate the existence of kingdoms in the southern Nile Valley coeval with Egypt itself, Kush enters history as an Egyptian province early in the New Kingdom.  With the disintegration of the New Kingdom in the 11th century BC, a state emerged centered at Napata (modern Karima, North Sudan).  Heavily Egyptianate in character, it became a rival to Egypt during the Third Intermediate Period and conquered its northern neighbor in the mid-eighth century, comprising the 25th dynasty of Egypt.

The Kushites were driven out of Egypt by Assyrian invasions in the early seventh century.  When Egypt regained its independence under the 26th dynasty, it began launching raids into Kush.  King Aspelta (ruled c. 600-580) moved the capital of Kush to Meroë, although dead kings continued to be interred at Napata until about 300 BC.

After conquering Egypt in 525, Cambyses II set off to invade Kush, but was forced to turn back when logistical problems resulted in many of his army starving.

Ethiopia was both a part and not a part of the Persian empire:  It was never conquered and retained native rulers, but was still involved enough that Darius seems to have regarded them as among his peoples (for example, at the table of nations at Naqš-e Rostam), so it is possible that Kush at least nominally acknowledged Persian suzerainty; alternately, the Kushites regarded the Persians as allies or neighbors in good standing.  Kush was not taxed, but according to Herodotus, it did send gifts every two years, amongst them ivory, seen prominently at the Persepolis apadana and used by Darius in the construction of the palace at Susa.

Ethiopians participated in Xerxes' invasion of Greece together with the Arabians under the command of Arsames, Darius' son by Artystone and thus the great king's half-brother (Herodotus, VII.69).  I cannot find testimony of which battles they participated in.

The Kushite throne was inherited matrilineally and thus most kings (qore) are considered to only probably be the sons of their predecessors.  They constructed stelae recording their deeds and regnal names, which were based on the Egyptian regnal naming system, and thus the names are known of most rulers of the kingdom (of which the first phase of the Meroitic period temporally corresponds to the Achaemenid period).  The queens or queen-mothers known as kandakes or kentakes also seem to have had an unusual degree of authority in the ancient world, and made a strong impression on Greeks and Romans in fighting on the frontier in the following centuries.

Kushite monarchs were buried in pyramids imitating the ancient Egyptian ones, though smaller and of different shape.  The burial chambers at the bases of these pyramids included reliefs describing the monarchs, stelae and some portions of the Book of the Dead.

The third-century AD "Alexander romance" tells that when Alexander invaded Egypt, he pressed south and only retreated upon seeing the strength of the Kushite armies.  However, more contemporary accounts of Alexander's life have him content to travel no farther south than the Siwa Oasis, and retreating in the face of a strong enemy strikes one as pretty out-of-character for him.  Arrian and Diodorus say that an embassy from Ethiopia visited Alexander in Babylon on his return from India in 323 BC.

Being essentially independent of Persia, Kush continued on its own throughout the Hellenistic period.  After the capital was fully moved to Meroë, the kingdom is recorded by that name in Graeco-Roman sources.  The country went into economic decline in the early centuries AD, possibly partly due to deforestation as the flourishing iron industry demanded a constant supply of charcoal.  In the fourth century, Meroë was conquered by the rising empire of Axum.

Around this time, the Nuba settled and began to found the Nubian kingdoms.  This was followed in the late Middle Ages by gradual Islamicization and Arabization of northern Nubia.  It was under Arab influence that the region acquired the name Sudan, said to derive from Bilad al-Sudan, "land of blacks," which makes an interesting latter-day reiteration of Aithiopia.  In the meantime, the Classical denotation ceased to be applied to Nubia and parts west, and was retained only in Axum, modern Ethiopia.

Language
Kushites presumably spoke an earlier phase of Meroitic, recorded from the third century BC onward in the Meroitic alphabet (prior to this, Egyptian hieroglyphs were used).  Meroitic is poorly-understood and of uncertain classification.  It went extinct around the turn of the fifth century AD with the spread of Nubian languages.

Religion
Kushites were polytheistic and shared many of the pantheon and certain beliefs with the Egyptians, as indicated by the use of the Book of the Dead.  Known deities specific to Kush included Apedemak and Dedun, Mandulis (apparently equated with Horus), and Arensnuphis, attested from the third century BC.

Clothing
Ethiopian clothing is shown at Persepolis and Naqš-e Rostam as including a cloak semicircling the body from the left under the arm and secured (probably with pins) over the shoulders, being left open down the right side.  It had a plain hem but its vertical edges were fringed.  The Ethiopian at Naqš-e Rostam wears a knee-length garment under his cloak, but whether it's a tunic or kilt is impossible to tell.  At Persepolis the Ethiopian delegation wear sandals of very open construction, secured by thongs over the heel and upper instep and just above the toes.  One member appears to be barefoot.  No headwear is attested.  Herodotus writes that Ethiopians at war dressed in lion and leopard skins, and painted their bodies with gypsum on one half and vermilion on the other.

A famous group of alabastrons (Greek alabaster vases) shows two black men in Iranian dress wearing tube-and-yoke corslets.  It is possible that they represent Kushites in the Persian military.  Rather than footed Medo-Persian trousers, they wear open-ankled ones of a looser cut typical of eastern Iranian peoples.

Weapons
Ethiopians were particularly well-known archers, known in early Egyptian writings as Ta-Seti, "people of the bow."  Herodotos says that their bows were made of strips of palm wood and were four cubits long (more than 80 inches/200cm), at which size they were presumably longbows rather than recurved.  Their arrows were "short" (mikroús) and stone-tipped.  The Museum of Fine Arts Boston's Warfare, hunting, & fishing category has examples of both early Napatan and Meroitic arrowheads, but (assuming the dating is all right) none specific to our period.

As for what to buy, Crazy Crow offers Neolithic bird points from America that are often very close in shape (both teardrop and barbed).  They're a bit too small and unfortunately you don't get to pick what they send you, but I would consider them acceptable as a non-custom item because no current production arrowheads I've been able to find come even that close.

Other Ethiopian weapons mentioned in Herodotus include spears pointed with whole, sharpened gazelle horns, and "studded clubs" (tr. Godley).  Additionally you will note in the MFA collection a number of stone maceheads.