ancient country in Central Asia; one of the Hellenistic states founded by the successors of Alexander the Great. It was situated between the Hindu Kush Mountains and the Oxus River (now Amu Darya) in what is now part of Afghanistan, Uzbekistan, and Tajikistan. A branch of the Hindu Kush Mountains separated it from the territories of the Sakas (Sacae), Iranian nomads. Its capital was Bactra, present-day Wazirabad (formerly Balkh), in north Afghanistan. Before the Greek conquest, Bactria was an eastern province of the Persian Empire.

Iranian peoples probably inhabited Bactria as early as the 8th century bc, and Bactra may have been the cradle of the Zoroastrian religion. Subjugated in the 6th century bc by Cyrus the Great of Persia, it became part of the Persian Empire. During his Persian conquest Alexander the Great conquered Bactria in 328 bc. It was, after his death, a part of the Seleucid Empire until 256 bc, when the Seleucid satrap Diodotus I (r. about 256–235 bc) established it as a separate kingdom. The kingdom was finally overrun by the Sakas about 130 bc, and then by the Kushans, who adopted Buddhism. In early medieval times the Bactrian region was known as Balkh and, since the 7th century ad, has been, along with the surrounding area, under heavy Islamic influence.