The first people known to have inhabited Central Asia were Scythians who came from the northern grasslands of what is now Uzbekistan, sometime in the first millennium BC; when these nomads settled in the region they built an extensive irrigation system along the rivers. At this time, cities such as Bukhoro (Bukhara) and Samarqand (Samarkand) emerged as centres of government and high culture. By the fifth century BC, the Bactrian, Soghdian, and Tokharian states dominated the region.