This seems to match the conquest of the Chen dynasty in southern China by Emperor Wen of Sui (r. 581-604). The Chinese "Old Book of Tang" and "New Book of Tang" mention (拂菻; i.e. Byzantium), which they equated with Daqin (i.e. the Roman Empire), beginning in 643 with an embassy sent by the king "Boduoli" (波多力, i.e. Constans II Pogonatos) to Emperor Taizong of Tang, bearing gifts such as red glass. These histories also provided cursory descriptions of Constantinople, its walls, and how it was besieged by "Da shi" (大食; the Arabs of the Umayyad Caliphate) and their commander "Mo-yi" (摩拽伐之; i.e. Muawiyah I, governor of Syria before becoming caliph), who forced them 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. Other Byzantine embassies in Tang China are recorded as arriving in 711, 719, and 742. From Chinese records it is known that Michael VII Doukas (Mie li sha ling kai sa 滅力沙靈改撒) of "Fu lin" dispatched a diplomatic mission to China's Song dynasty that arrived in 1081, during the reign of Emperor Shenzong of Song. Constantine IV would prove to be a much wiser and able Emperor than Constans II was. Like his predecessors, the wars with the Saracens continued relatively unabated. Before becoming Emperor, Constantine IV was the administrator of his father's lands for the eastern portions of the Empire, what few territories they were. They became fewer still when the Arabs began taking one Imperial Byzantine city after another along the coast of Ionia.