section_path: History/Tang dynasty (7th century)
section_name: Tang dynasty (7th century)
paragraph_text: Tang dynasty (7th century)
  
  Although the Silk Road was initially formulated during the reign of Emperor Wu of Han (141–87 BCE), it was reopened by the Tang Empire in 639 when Hou Junji conquered the Western Regions, and remained open for almost four decades. It was closed after the Tibetans captured it in 678, but in 699, during Empress Wu 's period, the Silk Road reopened when the Tang reconquered the Four Garrisons of Anxi originally installed in 640, once again connecting China directly to the West for land-based trade. The Tang captured the vital route through the Gilgit Valley from Tibet in 722, lost it to the Tibetans in 737, and regained it under the command of the Goguryeo-Korean General Gao Xianzhi.
  
  While the Turks were settled in the Ordos region (former territory of the Xiongnu), the Tang government took on the military policy of dominating the central steppe. The Tang dynasty (along with Turkic allies) conquered and subdued Central Asia during the 640s and 650s. During Emperor Taizong's reign alone, large campaigns were launched against not only the Göktürks, but also separate campaigns against the Tuyuhun, the oasis states, and the Xueyantuo. Under Emperor Taizong, Tang general Li Jing conquered the Eastern Turkic Khaganate. Under Emperor Gaozong, Tang general Su Dingfang conquered the Western Turkic Khaganate, an important ally of the Byzantine empire. After these conquests, the Tang dynasty fully controlled the Xiyu, which was the strategic location astride the Silk Road. This led the Tang dynasty to reopen the Silk Road, with this portion named the Tang-Tubo Road ("Tang-Tibet Road") in many historical texts.
  
  The Tang dynasty established a second Pax Sinica, and the Silk Road reached its golden age, whereby Persian and Sogdian merchants benefited from the commerce between East and West. At the same time, the Chinese empire welcomed foreign cultures, making it very cosmopolitan in its urban centres. In addition to the land route, the Tang dynasty also developed the maritime Silk Route. Chinese envoys had been sailing through the Indian Ocean to India since perhaps the 2nd century BCE, yet, it was during the Tang dynasty that a strong Chinese maritime presence could be found in the Persian Gulf and Red Sea into Persia, Mesopotamia (sailing up the Euphrates River in modern-day Iraq), Arabia, Egypt, Aksum (Ethiopia), and Somalia in the Horn of Africa.