One group of such nomads, the Yuezhi, were humiliated in battle in the 2nd century BCE by their bitter rivals the Xiongnu, who turned the Yuezhi's king's skull into a drinking cup, in fact. And in the wake of that, the Yuezhi migrated to Bactria and started the Kushan Empire in what is now Afghanistan and Pakistan. Although Silk Road trading began more than a century before the birth of Jesus, it really took off in the 2nd and 3rd centuries CE, and the Kushan Empire became a huge hub for that Silk Road trade. By then, nomads were being eclipsed by professional merchants who traveled the Silk Roads, often making huge profits. But those cities that had been founded by nomadic peoples became hugely important. They continued to grow because most of the trade on the Silk Road was by caravan, and those caravans had to stop frequently, you know, for like food and water and prostitutes. These towns became fantastically wealthy.