Religious beliefs of the peoples of the Silk Road changed radically over time and was largely due to the effects of travel and trade on the Silk Road itself. For over two thousand years the Silk Road was a network of roads for the travel and dissemination of religious beliefs across Eurasia.
The religious beliefs of people along the Silk Road at the beginning of the 1st century BCE were very different from what they would later become. When China defeated the nomadic Xiongnu confederation and pushed Chinese military control northwest as far as the Tarim Basin (in the 2nd century BCE), Buddhism was known in Central Asia but was not yet widespread in China nor had it reached elsewhere in East Asia. Christianity was still more than a century in the future. Daoism, in the strict sense of that term, connoting an organized religion with an ordained clergy and an established body of doctrine, would not appear in China for another three centuries. Islam would be more than seven centuries in the future.
The peoples of the Silk Road in its early decades followed many different religions. In the Middle East, many people worshiped the gods and goddesses of the Greco-Roman pagan pantheon. Others were followers of the old religion of Egypt, especially the cult of Isis and Osiris. Jewish merchants and other settlers had spread beyond the borders of the ancient kingdoms of Israel and Judea and had established their own places of worship in towns and cities throughout the region. Elsewherein the Middle East, and especially in Persia and Central Asia, many people were adherents of Zoroastrianism, a religion founded by the Persian sage Zoroaster in the 6th century BCE. It posited a struggle between good and evil, light and darkness; its use of fire as the symbol of the purifying power of good was probably borrowed from the Brahmanic religion of ancient India. The Greek colonies of Central Asia that had been left behind after the collapse of the empire of Alexander the Great had, by the 1st century BCE, largely converted from Greco-Roman paganism to Buddhism, a religion that would soon use the Silk Road to spread far and wide. In India, on side routes of the Silk Road that crossed the passes to the Indus Valley and beyond, the older religion of Brahmanism had given way to Hinduism and Buddhism; the former never spread far beyond India and Southeast Asia, while the latter eventually became worldwide in extent.
Coming at last to China on our west-to-east survey of the ancient faith of the Silk Road, we find that rulers worshipped their own ancestors in great ancestral temples; they were joined by commoners in also worshiping deities of the earth, the four directions, mountains and rivers, and many others. There was, as yet, in China no official state cult of Confucius, no Buddhism, and no organized religious Daoism. The beliefs of Korea and Japan at that early period are largely lost in an unrecorded past, but they appear to have been ancestral to the later Japanese religion of Shinto, a polytheistic belief system that emphasizes worship of local gods and goddesses, the importance of ritual purity, and rule by a king of divine descent.
That the religious beliefs of the peoples of the Silk Road change dradically from what they had been when trans-Eurasian trade began to take place on a regular basis was largely due to the effects of travel and trade on the Silk Road itself. Over the centuries for two thousand years the Silk Road was a network of roads for the travel and dissemination of religious beliefs across Eurasia. Religious belief is often one of the most important and deeply held aspects of personal identity, and people are reluctant to go where they cannot practice their own faith. Traders who used the Silk Road regularly therefore built shrines and temples of their own faiths wherever they went, in order to maintain their own beliefs and practices of worship while they were far from home. Missionaries of many faiths accompanied caravans on the Silk Road, consciously trying to expand the reach of their own religious persuasion and make converts to their faith.