The "Old Book of Tang" and "New Book of Tang" record that the Arabs ("Da shi" ) sent their commander Mo-yi (, pinyin: "Móyè", i.e. Muawiyah I, governor of Syria and later Umayyad caliph, r. 661–680 AD) to besiege the Byzantine capital, Constantinople, and forced the Byzantines to pay them tribute. The same books also described Constantinople in some detail as having strong granite walls and a water clock mounted with a golden statue of man. Henry Yule noted that the name of the Byzantine negotiator "Yenyo" (the patrician John Pitzigaudes) was mentioned in Chinese sources, an envoy who was unnamed in Edward Gibbon's account of the man sent to Damascus to hold a parley with the Umayyads, followed a few years later by the increase of tributary demands on the Byzantines. The "New Book of Tang" and "Wenxian Tongkao" described the land of Nubia (either the Kingdom of Kush or Aksum) as a desert south-west of the Byzantine Empire that was infested with malaria, where the natives had black skin and consumed Persian dates. In discussing the three main religions of Nubia (the Sudan), the "Wenxian Tongkao" mentions the Daqin religion there and the day of rest occurring every seven days for those following the faith of the "Da shi" (the Muslim Arabs). It also repeats the claim in the "New Book of Tang" about the Eastern Roman surgical practice of trepanning to remove parasites from the brain. The descriptions of Nubia and Horn of Africa in the "Wenxian Tongkao" were ultimately derived from the "Jingxingji" of Du Huan (fl. 8th century AD), a Chinese travel writer whose text, preserved in the "Tongdian" of Du You, is perhaps the first Chinese source to describe Ethiopia ("Laobosa"), in addition to offering descriptions of Eritrea ("Molin").