Dahae (Old Persian Dahâ): nomadic tribe in Central Asia. The name is also spelled Daai, Dai, or Daoi.
The Central-Asian steppe has been the home of nomad tribes for centuries. These nomads roamed across the plains and incidentally attacked the Achaemenid Empire. The Persians called these nomads the Sakâ, the Greeks knew them as the Scythians.
One of the tribes was known as the Dahâ, which is the Persian word for "robbers". This name need not surprise us; nomad tribes often received names like this from the people in the towns who suffered from their raids. For example, in the tenth century CE, the Europeans compared the Magyars to the greatest barbarians they had ever known, the Huns; when the Magyars finally settled, they kept using this name and their country is still called Hungary. Probably, "Dahâ" was a similar proud nickname.
A memory of these savage days seems to be preserved in the Avestan legend that the prophet Zarathustra, the founder of Zoroastroanism, was killed by the Dahae. In fact, this is impossible, because the Dahae and Zarathustra are separated by at least five centuries. However, it suggests that the atrocity of this particular tribe was proverbal.
The Dahae are mentioned for the first time in the Daiva inscription of the Persian king Xerxes (486-465); he mentions them as one of the satrapies that listened to his orders. Since they are not mentioned in any inscription by king Darius I the Great, we may assume that Xerxes subdued the Dahae.
The Greek researcher Herodotus calls the Dai a Persian nomad tribe:
The Persian nation contains a number of tribes, and the ones which Cyrus assembled and persuaded to revolt were the Pasargadae, Maraphii, and Maspii, upon which all the other tribes are dependent. [...] Other tribes are the Panthialaei, Derusiaei, Germanii, all of which are attached to the soil, the remainder - the Dai, Mardi, Dropici, Sagarti, being nomadic.note[Herodotus, Histories 1.125; tr.Aubrey de Selincourt.]
If this short catalogue goes back to an authentic list from the days of Cyrus the Great (559-530), we may assume that the Dahae took part in the rebellion against the Median leader Astyages in 550.
Being nomads, the Dahae were not living on one place. In the fourth century CE, they lived on the lower reaches of the river Syrdar'ya, the ancient Jaxartes. It is very probable that this was their homestead in Xerxes' days too, because he mentions the Dahae, the Sakâ haumavargâ and the Sakâ tigrakhaudâ in one breath, and these two tribes certainly lived in this neighborhood. In the age of the Macedonian king Alexander the Great, they lived in the neigborhood of Hyrcania.
The Dahae were famous for their mounted archers. When Alexander the Great tried to subject the Achaemenid empire, the Dahae loyally supported the Persian king Darius III during the battle of Gaugamela (1 October 331). When this king was killed by Bessus (a nobleman who wanted to continue the struggle against the invaders), the Dahae sided with him, and - later - with the Iranian warlord Spitamenes. Later, they switched allegiance to Alexander, and they played a very important role in his conquest of the Punjab.
The tribe of the Dahae disintegrated after the fall of the Achaemenid empire. Older sub-tribal formations became independent tribes, such as the Xanthians and Pissyri. Another tribe was that of the Parni, who went south in the third century BCE and founded the Parthian empire. In 155, they subjected what was left of the "mother tribe".