It was located on high ground for defensive reasons, south of a river valley and north of a large fertile area which has now became part of the city of Samarkand.
https://en.wikipedia.org/wiki/Afrasiyab_(Samarkand)
The habitation of the territories of Afrasiyab began in the 7th-6th century BC, as the centre of the Sogdian culture.
Scholars consider Afrasiab to be a distortion and a corrupted form of the Tajik word Parsīāb (from Sogdian Paršvāb), meaning "beyond the black river", the river being Sīāhāb or Sīāb, which bounds the site to the north. Afrā is the poetic form of the Persian word Farā (itself a poetic word), which means 'beyond, further', while Sīāb comes from sīāh meaning 'black' and Āb meaning 'water; river; sea' (depending on the context).
http://www.iranicaonline.org/articles/afrasiab-the-ruined-site
"In Moḥarram, 617/March, 1220 Samarqand was seized by the army of Čingiz Khan and destroyed. After that event life in Afrāsīāb never recovered, and the town became a ruined site. In the 9th/15th century Afrāsīāb is mentioned under the name of Bālā Ḥeṣār as a “fortress of former days.” "
Khiva Fortress, Khiva, Uzbekistan
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