The earliest Bronze Age colonists of the Tarim Basin were people of Caucasoid physical type who entered probably from the north and west and probably spoke languages that could be classified as Pre- or Proto-Tocharian, ancestral to the Indo-European Tocharian languages documented later in the Tarim Basin. These early settlers occupied the northern and eastern parts of the Tarim Basin, where their graves have yielded mummies dated about 1800 BC. They participated in a cultural world centered on the eastern steppes of central Eurasia, including modern northeastern Kazakhstan, Kyrgyzstan, and Tajikistan.
At the eastern end of the Tarim Basin, people of Mongoloid physical type began to be buried in cemeteries such as Yanbulaq some centuries later, during the later second or early first millennium BC. About the same time, Iranian-speaking people moved into the Tarim Basin from the steppes to the west. Their linguistic heritage and perhaps their physical remains are found in the southern and western portions of the Tarim. These three populations interacted, as the linguistic and archaeological evidence reviewed by Mallory and Mair makes clear, and then Turkic people arrived and were added to the mix.
The first people known to inhabit Central Asia were Iranian nomads who arrived from the northern grasslands of what is now Uzbekistan sometime in the first millennium BC. These nomads, who spoke Iranian dialects, settled in Central Asia and began to build an extensive irrigation system along the rivers of the region. At this time, cities such as Bukhoro (Bukhara) and Samarqand (Samarkand) began to appear as centers of government and culture. By the 5th century BC, the Bactrian, Soghdian, and Tokharian states dominated the region.
As China began to develop its silk trade with the West, Iranian cities took advantage of this commerce by becoming centers of trade. Using an extensive network of cities and settlements in the province of Mawarannahr (a name given the region after the Arab conquest) in Uzbekistan and farther east in what is today China's Xinjiang Uygur Autonomous Region, the Soghdian intermediaries became the wealthiest of these Iranian merchants. Because of this trade on what became known as the Silk Route, Bukhoro and Samarqand eventually became extremely wealthy cities, and at times Mawarannahr was one of the most influential and powerful Persian provinces of antiquity.