also called BACTRIANA, or ZARIASPA, ancient country lying between the mountains of the Hindu Kush and the Amu Darya (ancient Oxus River) in what is now part of Afghanistan, Uzbekistan, and Tajikistan. Bactria was especially important between about 600 BC and about AD 600, serving for much of that time as a meeting place not only for overland trade between East and West but also for the crosscurrents of religious and artistic ideas. Bactria's capital was Bactra, also called Bactra-Zariaspa (modern Balkh, Afghanistan). Bactria was a fertile country, and a profusion of mounds and abandoned water channels testifies to its ancient prosperity.

The first written records of Bactria are Achaemenian. The region was probably subdued by Cyrus II the Great in the 6th century BC and remained an Achaemenian province for the next 200 years. When Alexander the Great defeated Darius III, the Bactrian satrap, Bessus, tried unsuccessfully to organize resistance in the East. Upon the death of Alexander (323 BC) Bactria passed under the rule of Seleucus I Nicator.

About 250 BC either Diodotus, the Seleucid satrap of Bactria, or his son of the same name founded an independent kingdom. The Seleucid king Antiochus III the Great defeated their successor, the usurper Euthydemus, but continued to recognize his independence. Euthydemus' successors advanced into the Hindu Kush and northwestern India, where they established the Indo-Greek branch of the kingdom. At the height of their power they ruled almost all of what is now Afghanistan, parts of Central Asia, and a large area in Pakistan. Consequently, Hellenistic influence on the culture of Central Asia and northwestern India has been considerable. Hellenistic traditions are especially evident in art, architecture, coinage, and script.

Sometime before 128 BC Greek rule north of the Hindu Kush was challenged by a people known to the Chinese as the Yueh-chih. By 128 BC the Greeks had become Yueh-chih tributaries, and soon afterward the Yueh-chih occupied Bactria. They probably were an Iranian people and included the Tocharoi, whose name was subsequently applied to the whole area (Tocharian kingdom). In the 1st century AD the new rulers of Bactria extended their rule into northwestern India; that movement is associated with a group known as the Kushans, under whom the country became a centre of Buddhism. In the latter half of the 4th century the Hephthalites (originally a tribe of the Yueh-chih) settled in Bactria, and for almost two centuries they engaged in wars with the Sasanians. In AD 565 the western Turks overthrew the Hephthalites and ruled the area until the Muslim conquest in the middle of the 7th century.