largest seaports in the world, hosting foreign travelers throughout maritime Asia. At the time, Guangzhou was a major port along the maritime silk road and involved in heavy trade with Japan. The Tang capital city of Chang'an became well known as a multicultural metropolis filled with foreign travelers, dignitaries, merchants, emissaries, and missionaries. Chinese Buddhist monks such as Xuanzang (died 664) continued to travel abroad to places like India in order to gain wisdom, collect Buddhist relics, and translate additional sutras into Chinese. Although the reign of Emperor Xuanzong (r. 712–756) is seen as the zenith point of the Tang dynasty, it was during the last years of his reign that one of the most destructive rebellions in Chinese history occurred. The Tang Empire had recruited many Central Asian Turks into their armed forces. One of these was An Lushan (703–757), a Sogdian-Turk who became a military commander and personal favorite of Emperor Xuanzong's concubine Consort Yang. He instigated the An Lushan Rebellion, which caused the deaths of millions of people, cost the Tang dynasty their Central Asian possessions, and allowed the Tibetans to invade China and temporarily occupy the capital, Chang'an. The Tang dynasty recovered under Emperor Xianzong (805-820) but it never achieved its former martial and political strength. The unintended effect of the rebellion, however, was the loosening of government restrictions on trade. Although the 9th century was politically turbulent, the economy of China actually continued to thrive, bolstered still by foreign trade. The Japanese were sending embassies to the Tang Empire as late as 894, which was finally halted by Emperor Uda by the persuasion of Sugawara no Michizane. Five Dynasties and Ten Kingdoms The Five Dynasties and Ten Kingdoms (907-960) period was an age of division and Chinese civil war between the unified Tang and Song dynasties. It is notable for the introduction of Greek Fire (or a formula similar to the original) from Chinese contacts in Arabia. Greek Fire was then applied to the new Chinese invention of the double-piston pump flamethrower, used in battle during the Five Dynasties era and Song dynasty. Song dynasty The Chinese political theory of China being the center of world diplomacy was largely accepted in East Asia, except in periods of Chinese weakness such as the Song dynasty (960-1279). During the Northern Song dynasty (960-1279), the Chinese emperors were forced to accept the emperors of the Khitan-led Liao dynasty,