The administration of Persia was regulated by an actual survey of the people, the cattle, and the fruits of the earth; and this monument, which attests the vigilance of the caliphs, might have instructed the philosophers of every age.
The flight of Yezdegerd had carried him beyond the Oxus, and as far as the Jaxartes, two rivers of ancient and modern renown, which descend from the mountains of India towards the Caspian Sea.

He was hospitably entertained by Tarkhan, prince of Fargana, a fertile province on the Jaxartes: the king of Samarcand, with the Turkish tribes of Sogdiana and Scythia, were moved by the lamentations and promises of the fallen monarch; and he solicited, by a suppliant embassy, the more solid and powerful friendship of the emperor of China.

The virtuous Taitsong, the first of the dynasty of the Tang may be justly compared with the Antonines of Rome: his people enjoyed the blessings of prosperity and peace; and his dominion was acknowledged by forty-four hordes of the Barbarians of Tartary.

His last garrisons of Cashgar and Khoten maintained a frequent intercourse with their neighbors of the Jaxartes and Oxus; a recent colony of Persians had introduced into China the astronomy of the Magi; and Taitsong might be alarmed by the rapid progress and dangerous vicinity of the Arabs.

The influence, and perhaps the supplies, of China revived the hopes of Yezdegerd and the zeal of the worshippers of fire; and he returned with an army of Turks to conquer the inheritance of his fathers.