Sogdian is an extinct Indo-Iranian language that was spoken in Sogdiana—the Zarafshan River Valley—located in modern day Uzbekistan and Tajikistan. The major cities were Samarkand, Panjakent, and Fergana. Sogdian was an important language of culture and trade until about the 10th century, when it declined and eventually became extinct. •See also Indo-Iranian languages. Ref: Wikipedia, Origin of the Indo-European languages: Part IV