Ancient country of Central Asia. It was centred in the fertile valley of the Zeravshan River, in present-day Uzbekistan. It became a satrapy of the Achaemenian dynasty under Darius I in the 6th century BC and was conquered by Alexander the Great in the 4th century. It asserted its independence from the Seleucid dynasty circa 250 BC as part of the kingdom of Bactria and fell to invading northern tribes in the 2nd century BC. It prospered as a centre of Islamic civilization, especially under the Sāmānid dynasty (9th–10th centuries AD), until the Mongol invasion of the 13th century. Seealso Bukhara.
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