structural:scholar_edition
Contacts with the Byzantine Empire

The Old Book of Tang and New Book of Tang mention several embassies made by Fu lin (拂菻; i.e. the Byzantine Empire), which they equated with Daqin (which may refer to the Roman Empire or Middle East), beginning in 643 with an embassy sent by the king Boduoli (波多力, i.e. Constans II Pogonatos) to Emperor Taizong, bearing gifts such as red glass and green gemstones. These histories also provided cursory descriptions of Constantinople and its walls, as well as how it was besieged by Da shi (大食; the Arabs of the Umayyad Caliphate) and their commander "Mo-yi" (摩拽; i.e. Muawiyah I, governor of Syria before becoming caliph), who forced the Byzantines to pay tribute. Henry Yule highlights the fact that Yazdegerd III (r. 632–651), last ruler of the Sasanian Empire, sent diplomats to China for securing aid from Emperor Taizong (considered the suzerain over Ferghana in Central Asia) during the loss of the Persian heartland to the Islamic Rashidun Caliphate, which may have also prompted the Byzantines to send envoys to China amid their recent loss of Syria to the Muslims. Tang Chinese sources also recorded how Sassanid prince Peroz III (636–679) fled to Tang China following the conquest of Persia by the growing Islamic caliphate.

The expansion of China's power into Central Asia under Emperor Taizong seems to have been noticed in the West. Theophylact Simocatta, a Byzantine Greek historian during the reign of Heraclius (r. 610–641), wrote that Taugast (or Taugas; Old Turkic: Tabghach, from Tuoba, the Xianbei clan of Northern Wei), was a great eastern empire in the Far East that ruled over Turkic people, with a capital city roughly 1,500 miles northeast from India that he called Khubdan (from the Turkic word Khumdan, meaning, Chang'an), where idolatry was practiced but the people were wise and lived by just laws. He depicted the Chinese empire as being divided by a great river (i.e. the Yangzi) that served as the boundary between two rival states at war, yet during the reign of Byzantine Emperor Maurice (582–602 AD) the northerners wearing "black coats" conquered the "red coats" of the south (black being a distinctive color worn by the people of Shaanxi, location of the Sui capital Sui Chang'an, according to the 16th-century Persian traveler Hajji Mahomed, or Chaggi Memet). This account may correspond to the conquest of the Chen dynasty and reunification of China by Emperor Wen of Sui (r. 581–604). Simocatta names their ruler as Taisson, which he claimed meant Son of God, either correlating to the Chinese Tianzi (i.e. Son of Heaven) or even the name of the contemporary ruler Emperor Taizong.