The legend of Arash the great Bowman
The legend runs as follows: In a war between the Iranians and the Turanians over the "royal glory" (Khwarrah), the great Afrasiab (King of the Turan) had hounded the forces of the Iranian King Manuchehr, finally the two sides agreed to make peace.
Both reach an agreement that whatever land falls within the range of a bow-shot shall be returned to the Iranians, and the rest should then fall to Afraisab and the Turanians (Khwarezm).
An angel al-Biruni calls 'Esfandaramad' instructs Manuchehr to construct a special bow and arrow, and his best archer Arash is asked to be fire a specially prepared arrow at dawn, which reputedly traveled a great distance (see below) before finally landing and so marking the future border between the Iranians and the Turanians.
In al-Tabari, Arash is exalted by the people, is appointed commander of the archers and lives out his life in great honor. The distance the arrow travels varies: in one it is thousand leagues (farsakhs), in another forty days walk. In several, the arrow traveled from dawn to noon, in others from dawn until sunset. According to al-Biruni, it hit a nut tree between "Fargana" and "Tabaristan" in the furthest reaches of [Greater] Khorasan"
A few sources specify a particular date for the event. The Middle ages Mah i Frawardin notes the 6th day of the 1st month (i.e. Khordad of Frawardin); later sources associate the event with the name-day festivities of Tiregan (13th of Tir) - tir meaning "arrow."
The location from which Arash fired his arrow varies as well. In the Avesta it is 'Airyo khshaotha', a not-further identified location in the Middle Clime. Islamic-era sources typically place the location of the shot somewhere just south of the Caspian Sea, variously in Tabaristan (Tabari, Talebi, Maqdesi, ibn al-Atir, Marashi); a mountain-top in Ruyan (al-Biruni, Gardizi), Amul fortress (Mojmal), Mount Damavand (Balami) or Sari (Gorgani).
The place the arrow landed is variously identified as 'Mount Khvanvant' in the Avesta (likewise an unknown location); a river in Balkh (Tabari, al-Atir); east of Balkh (Talebi); Bactria/Tokharistan (Maqdesi, Gardizi); the banks of the Oxus River (Balami) or Merv (Mojmal).
Source(s):
http://en.wikipedia.org/wiki/Arash
The Turan
In the Avesta the term Turanians was a collective name for the eternal enemies of Zoroastrism, who it associated with the Khwarezm ruler Afrasiab (ca. 305-? AD) called Franrasyan in the Avesta hymns.
The Turan is historically considered the territory that is located north and east of Amy-Darya, once populated by nomadic Turanians variously called Sakas, Masguts, Massagetae, Kushans, Parthians, Ephtalites and other names of the consecutively Scythian, Hunnic, and Türkic tribes.
The peoples of the Turan consisted of symbiotic combination of agricultural settlers of oases and river valleys, and nomadic and semi-nomadic population engaged in animal husbandry in the deserts and steepes.