Transoxiana was the largest country outside the limits of Iran proper that was from early times inhabited by Iranian peoples - either as settled agriculturists (the Sogdians and the Chorasmians) or as nomads (the Sakas). Owing to its geographical situation it came only in particular periods into the field of vision of those peoples who have left us historical chronicles and other forms of written sources. In reconstructing the political history of Transoxiana between the 3rd century B.C. and the 7th century A.D. it is necessary to take into account not only the fragmentary character of the information at our disposal, but also the point of view from which Transoxiana is being mentioned or described.

From the last quarter of the 4th century B.C. down to the middle of the 2nd century B.C. we see the land beyond the Oxus mainly through the eyes of Greek and Latin writers (Strabo, Arrian, Diodorus, Quintus Curtius Rufus, Pompeius Trogus in Justin's epitome, Ptolemy, Pliny and others), as the far north-eastern edge of the civilized world.

From the latter part of the 2nd century B.C. to the beginning of the 3rd century A.D. we are submitted to the ideas and impressions of the court historiographers of the Celestial Empire, the writers of the Shih-chi, Han shu and Hou Han-shu, whose “Sinocentrism” was not at all confined merely to their geographical view from the east.

Starting in the 3rd century A.D., we must either consider Transoxiana from the standpoint of the Sasanian kings (Shāpūr I's inscription on the Ka‘aba-yi Zardusht, and other Sasanian inscriptions) who carried out expeditions beyond the Oxus and obviously did not try to play down their successes, or follow the official historiography of the late Sasanian period, as reflected in Islamic sources, such as Tabarī.