Ṭabari (q.v.; d. 923) knew about the quadripartition of the army that he considered to have taken place during the reign of Khosrow I (q.v.; r. 531-79), and he wrote that there was an iṣbahbadh of the East, one of the West, one in charge of Nimruz, and one of Azarbaijan (Ṭabari, tr., V, p. 149); similar information is found also in the works of other Islamic historiographers. Thanks to this combined evidence, we know that one of the four mighty armies that defended the empire in late Sasanian times, after the military and administrative reform begun by Kawād I (q.v.; r. 488-531) and completed by Khosrow I, was the army of the East (Xwarāsān), attesting that this name was current in the official language of the Sasanian government. However, chances are that it did not designate any specific region, province or civil administration; rather it is by now clear that it pointed to a specific geographical area in military administration (see already Gnoli, 1985 contra Gignoux, 1984).

The “side of the East” is also one of the quarters of the Sasanian Empire according to the Middle Persian geographical treatise Šahrestānīhā ī Ērānšahr (q.v.), written well into the Islamic period, under ʿAbbasid (q.v.) rule, though definitely preserving late Sasanian lore. When looking at this text as a whole, one cannot help but notice that the southern quarter is far larger than the other ones, including areas that one may think better placed in Xwarāsān, and that the northern one is comparatively smaller than what one would expect (Marquart, 1931; Daryaee; see also Gyselen, 1988 for a critical evaluation of its contents). The kust ī Xwarāsān is the first sector of the empire to be listed in this text. According to its anonymous author, the “East” includes: Samarkand that was in Sugud ī haft āšyān ‘Sogdiana of the seven abodes’, Nawāzag in Baxl ī bāmīg ‘Splendid Balkh’, Xwārazm, Marwrōd, Marw, Harē(w), Pūšang, Tōs, Nēwšābuhr, Kāyēn, Dahestān in Gurgān, and Kūmīs (pars. 2-18).

Moreover, paragraphs 19-20 of the Šahrestānīhā contain the name of five cities built by Husraw (Khosrow I): Husraw-šād, Husraw-mūstābād, Wisp-šād-Husraw, Hubōy-Husraw, and Šād-farrox-Husraw, specifying that this conurbation was surrounded by a long wall. Nothing is known about the whereabouts of these cities, but there is no formal reason not to include them in Xwarāsān (Gyselen, 1988, p. 198), though Joseph Marquart (1931, p. 13) and Touraj Daryaee (pp. 40-41) lean toward moving them to the western quarter (kust ī xwarwarān). When comparing the toponyms found in the Šahrestānīhā with the evidence provided by Sasanian administrative glyptics one immediately notices that only a few of the geographical names mentioned in the Šahrestānīhā are also found on seals and sealings and that some of the provinces attested in the Middle Persian text, such as Sogdiana, Bactria or Chorasmia (qq.v.), were not part of the late Sasanian Empire (Gyselen, 1988, p. 193).

Another list of the provinces of Khorasan in the Sasanian era is preserved in a work traditionally assigned to the Armenian geographer and historian Movsēs Xorenacʿi (q.v.; Marquart, 1901, pp. 47-93). The toponyms found in this record only partly coincide with those enumerated in the Middle Persian text. Moreover, both the sequence in which they are listed and some of the toponyms themselves seem to be out of order, suggesting that some mishap may have occurred when writing or copying the Catalogue.

Furthermore, Islamic authors such as Ebn Ḵordāḏbeh (q.v.; d. ca. 885) knew of a division of Khorasan into four distinct marzbanates in Sasanian times (Marquart, 1901, p. 70). Another piece of evidence pointing toward the likelihood of a geographic notion identifying the East in the late Sasanian period comes from numismatics. Coins minted in Umayyad Zāvulistān (Zābolestān) after 687 CE on a Sasanian model carry the legend tkyn’ bg hwtʾy hwlʾsʾn MLKA (Tegīn bay xwadāy Xwarāsān šāh ‘Tegin, His Majesty, Lord, King of Khorasan’) attesting the title Xwarāsān šāh in the very early Islamic period (Gyselen, 2010, p. 237; Rezakhani, 2017, p. 168).

As is well known, Islamic Khorasan includes much of the eastern Iranian world that in the scholarly literature dealing with the pre-Islamic period is typically defined as outer Iran, a region further away from the centers of power of Mesopotamia and Persia that were better known to classical historians due to their closeness to the western world. Nonetheless, the eastern expanse has always been a vital part of the Iranian ecumene. In the Bisotun inscription (q.v.), Darius the Great (q.v.; r. 522-486 BCE) states that he rules over twenty-three countries, among which were the eastern ones of … ParΘava, Zranka, Haraiva, Uvārazmī, Bāxtriš, Suguda, Gandāra, Saka, θataguš , Harauvatiš… ‘… Parthia, Drangiana, Aria, Chorasmia, Bactria, Sogdiana, Gandāra, Scythya, Sattagydia, Arachosia…’ (Schmitt, pp. 49-50), each of which came at some point in history to be considered to be part of Khorasan.

Similar lists are found in other inscriptions by Darius in Susa and Persepolis (qq.v.) as well as of Xerxes I (r. 486-65 BCE; XPh, daiva inscription). When the Achaemenid Empire fell under the blows of Alexander (q.v.) and his Macedonians, opening the way for the blossoming of Hellenism in Western Asia, the heartland of Iranism moved toward the East. There, in the flatlands to the east of the Caspian Sea (q.v.), Arsaces rose in revolt against the Seleucids (q.v.), soon to conquer Parthia at the head of his Parni (APARNA, q.v.) kinsmen, taking advantage of the havoc caused by Andragoras’ (q.v.) short lived rebellion and of the defeat of the former Seleucid governor. A few years later Diodotus (q.v.), the Seleucid satrap of Bactria-Sogdiana, obtained his independence (Cereti, pp. 236-39). The earlier part of history of the Greek kingdoms of Central Asia and of the kings who later moved toward the territories to the south of the Hindu Kush (q.v.) is only known in its very general outlines (Bernard, pp. 99-101), but these people left an impressive cultural heritage to the Kushans (q.v.), who between the first and third centuries CE became one of the major powers in Eastern Iran and Northern India (Bivar; Falk). The Kushans were able to deal on an equal hand with the Arsacids (q.v.) and were certainly instrumental in keeping alive the Hellenistic heritage while integrating it in the new cultural context, as witnessed among others by the use of the Greek alphabet to write the Bactrian language (q.v.).

Like the Achaemenids, the early Sasanian kings also claimed authority over Eastern Iran. In his renowned trilingual inscription on the Kaʿba-ye Zardošt (q.v.), Šāpur I (q.v.; r. 239-70) mentions the eastern lands of *[Par] Θaw (…) ud hamag Parišxwār kōf, Māδ, Wurgān, Marγ, Harēw, ud hamag Abaršahr, Kermān, Sagestān, Tuγrān, Mak(u)rān, Pār(a)dān, Hindestān, Kušānšahr yad fraxš ō Paškabūr ud yad ō Kāš, Suγd ud Čāčestān [ud až hō (?) ārag zrē]h Mazū[n] šahr ‘Parthia (…) the entire Alborz chain, Media, Gurgān, Marw, Harēw, the entire Abaršahr, Kermān, Sistān, Turān, Makrān, Pāradān, Hindestān, Kušānšahr up to Pešāwar and to Kāšγar (?), Sogdiana and Taškent and on the other side of the sea the land of Mazūn [Oman]’ (Huyse, I, pp. 22-24; the quote follows the better preserved Parthian text). By doing so, he lays claim to lordship over the whole of later Khorasan. Most interesting is Šāpur’s mentioning Kušānšahr, a province that was then ruled by the Kushano-Sasanian dynasty, probably a cadet branch of the Sasanian family that enjoyed a high degree of autonomy. These dynasts began minting coins almost contemporarily with the Sasanian Ardašīr I (q.v.; d. 242 CE; Rezakhani, pp. 72-86; on Kushano-Sasanian coinage, see Jongeward and Cribb).

The latter part of the Sasanian period was characterized by a growing confrontation of the empire with aggressive eastern foes, who, wave after wave, threatened the oriental frontiers. Unfortunately we have relatively few written documents on the history of the Iranian Huns, Kidarites, Alkhan, Hephthalites, Nēzak (qq.v.), and of the Turkish groups that followed in their wave (Rezakhani, pp. 87-184), though some information may come from Chinese sources (see Daffinà on Chinese sources for Sasanian history). Nonetheless, numismatic research has made it possible to reconstruct at least the outline of the reigns of these powerful foes of the Sasanian empire, who were deeply influenced by their western neighbor and its culture (Göbl; Vondrovec; Alram and Klimburg-Salter, 1999; Alram et al., 2010).

The Kidarites (ca. 370-467 CE) settled in Bactria already in the 4th century CE and by 370 they were running the administrative divisions of the Sasanian empire in that area. They were followed by a second wave of nomads, the Alkhan (ca. 440-500 CE), who by 380 had taken over the Sasanian mint in Kabulistān to later expand their power to the east and then south toward the Indian plains. Among the Iranian Huns, the Hephthalites (ca. 484-560 CE) were a mighty foe of the Sasanians. In 484 Pērōz (see FIRUZ, r. 459-84) was heavily defeated by this eastern enemy and it was only Khosrow I who avenged this defeat in 560, putting an end to Hephthalite power through an alliance with the western Turks, who were bound to play an important political role in the area in the years to come. The late fifth century also saw the rise of the Nēzak (ca. 480-560 CE) in Zābulistān and then Kabulistān (Alram, 2016, pp. 18 ff.).

This interaction—military, social, and cultural—deeply transformed eastern Iran, preparing the ground for the intellectual renaissance that was to take place in the Islamic era.

Eastern Iran was Zoroaster’s (q.v.) motherland and the Avesta (q.v.) preserves a wealth of precious information on early society in an area stretching from the Aral Sea to Helmand (qq.v.) province in southern Afghanistan (Skjærvø; on Avestan geography and Zoroaster’s homeland see Gnoli, 1980, pp. 59-158; and AVESTAN GEOGRAPHY) that was to have a powerful influence on the development of later Iranian culture and lore. Central Asia has always been a crossroads of different religious traditions and has preserved a rich heritage of Buddhist, Christian, and Manichaean texts written in a variety of languages that have allowed scholars to better understand these religions. It is precisely this multicultural environment that blossomed into a veritable Age of Enlightenment in the Iranian world (Starr). Nor can one underestimate the powerful impact that the Sistanian epic cycle, rich in common Eastern Iranian elements, had on later Persian literature (Hameen-Antilla, pp. 174-199; Gazerani; van Zutphen).