Chinese knowledge of India began to open up as early as the 2nd century BC, as Han emissaries visited Central Asian countries like Bactria, Sogdia and Persia and brought back reports of more distant regions, including Sindh in India. Silk Road trade and the spread of Buddhism into China starting from the 1st century AD brought closer ties, as Indian Buddhists went to China to proselytize and Chinese Buddhists went to India to study or acquire religious texts. The 7th-century Great Tang Records of the Western Regions, a travelogue by the Chinese monk Xuanzang, is a major source in the study of India at that time. Maritime trade between South China, Southeast Asia and the east coast of India also flourished throughout the middle ages.