WEBEmperor Xuanzong of Tang. Emperor Xuanzong of Tang ( [ɕwàn.tsʊ́ŋ]; [8] 8 September 685 [5] [9] – 3 May 762 [6] ), personal name Li Longji, [10] was an emperor of the Tang dynasty of China, reigning from 712 to 756 CE. His reign of 44 years was the longest during the Tang dynasty.