For a long time, Kucha was the most populous oasis in the Tarim Basin. As a Central Asian metropolis, it was part of the Silk Road economy, and was in contact with the rest of Central Asia, including Sogdiana and Bactria, and thus also with the cultures of South Asia, Iran, and coastal areas of China. Its main population was Indo-European, part of the ancient population of the Tarim Basin known as Tocharians, and they spoke an Indo-European language known as Tocharian. Chinese sources from the 2nd century BCE did mention Indo-European Wusun populations with blue eyes and red hair in the area of the Ili river, to the northwest of Kucha. Zhang Qian traveled the area westward to visit Central Asia, during the 2nd century BCE, stopping at Kucha. The Roman Maes Titianus is known to have visited the area in the 2nd century CE. According to the "Book of Han" (completed in 111 CE), Kucha was the largest of the "Thirty-six Kingdoms of the Western Regions", with a population of 81,317, including 21,076 persons able to bear arms. The Kingdom of Kucha occupied a strategic position on the Northern Silk Road, which brought it prosperity, and made it a wealthy center of trade and culture.