The beginnings of the Silk Roads lay in both geography and history. As a geographic unit, Eurasia is often divided into inner and outer zones that represent quite different environments. Outer Eurasia consists of relatively warm, well-watered areas, suitable for agriculture, which provided the setting for the great civilizations of China, India, the Middle East, and the Mediterranean. Inner Eurasia—the lands of eastern Russia and Central Asia—lies farther north and has a harsher and drier climate, much of it not conducive to agriculture. Herding their animals from horseback, the pastoral people of this region had for centuries traded with and raided their agricultural neighbors to the south. Products of the forest and of semi-arid northern grasslands known as the steppes—such as hides, furs, livestock, wool, and amber—were exchanged for the agricultural products and manufactured goods of adjacent civilizations. The movement of pastoral peoples for thousands of years also served to diffuse Indo-European languages, bronze metallurgy, horse-based technologies, and more all across Eurasia.

The construction of the second-wave civilizations and their imperial states during the last five centuries B.C.E. added another element to these earlier Eurasian connections. From the south, the Persian Empire invaded the territory of pastoral peoples in present-day Turkmenistan and Uzbekistan. From the west, Alexander the Great’s empire stretched well into Central Asia. From the east, China’s Han dynasty extended its authority westward, seeking to control the nomadic Xiongnu and to gain access to the powerful “heavenly horses” that were so important to Chinese military forces. By the early centuries of the Common Era, indirect trading connections, often brokered by pastoral peoples, linked these Eurasian civilizations in a network of transcontinental exchange.

Silk Road trading networks prospered most when large and powerful states provided security for merchants and travelers. Such conditions prevailed during the second-wave era when the Roman and Chinese empires anchored long-distance commerce at the western and eastern ends of Eurasia. Silk Road trade flourished again during the seventh and eighth centuries C.E. as the Byzantine Empire, the Muslim Abbasid (ah-BAH-sihd) dynasty, and Tang dynasty China created an almost continuous belt of strong states across Eurasia. In the thirteenth and fourteenth centuries, the Mongol Empire briefly encompassed almost the entire route of the Silk Roads in a single state, giving a renewed vitality to long-distance trade. Over many centuries, various technological innovations, such as yokes, saddles, and stirrups, made the use of camels, horses, and oxen more effective means of transportation across the vast distances of the Silk Roads.