The Azerbaijanis of Iran are believed to be descended from various groups, including Mannaeans, an ancient people who lived in the territory of present-day northwestern Iran to the south of Lake Urmia at around the 10th to 7th centuries BC, and spoke a dialect related to Hurrian (a non-Semitic and non-Indo-European language related to Urartian), and the Medes, an ancient Iranian ethnic group which, under the rule of King Cyaxares, established the Median Empire and came to dominate the region. The Median Empire is believed to have conquered and assimilated the Mannaeans by the 6th century BC. Historical research suggests that the Old Azeri language, belonging to the Northwestern branch of the Iranian languages and believed to have descended from the language of the Medes, gradually gained currency and was widely spoken in said region for many centuries.