The earliest historically attested populations of Anatolia were the Hattians in central Anatolia, and Hurrians further to the east. The Hattians were an indigenous people, whose main center was the city of Hattush. Affiliation of Hattian language remains unclear, while Hurrian language belongs to a distinctive family of Hurro-Urartian languages. All of those languages are extinct; relationships with indigenous languages of the Caucasus have been proposed, but are not generally accepted. The region became famous for exporting raw materials. Organized trade between Anatolia and Mesopotamia started to emerge during the period of the Akkadian Empire, and was continued and intensified during the period of the Old Assyrian Empire, between the 21st and the 18th centuries BCE. Assyrian traders were bringing tin and textiles in exchange for copper, silver or gold. Cuneiform records, dated circa 20th century BCE, found in Anatolia at the Assyrian colony of Kanesh, use an advanced system of trading computations and credit lines.