Christian priests in particular) Arka′un or Erke′un, which was later applied for Christians in general (including Roman Catholics) whereby Christianity was named in Chinese as 也里可溫教 (Yělǐkěwēn jiào). However, there is a suggestion that the term Yělǐkěwēn jiào might be used also for Míng jiào and some other religions in Jiangnan. History The Church of the East had significant evangelical success under the Mongol Empire. Despite the Abbasid caliphate sending soldiers to fight against An Lushan with the Tang dynasty and the fact that General Guo Ziyi fought on the Tang dynasty side against An Lushan, Guo Ziyi's descendants joined the Mongol empire's army and his direct descendant Guo Kan was instrumental in the Mongol Siege of Baghdad (1258) and the destruction of the Abbasid caliphate which saw the execution of the last Abbasid caliph and the slaughter of 800,000-2,000,000 Arab Muslim civilians in Baghdad, with only the Nestorian Assyrian Christians being spared. The rise of the Mongol-led Yuan dynasty in the 13th century allowed the church to return to China. By the end of the century two new metropolitan provinces had been created for China: Tangut and 'Katai and Ong'. The province of Tangut covered northwestern China, and its metropolitan seems to have sat at Almaliq. The province evidently had several dioceses, even though they cannot now be localised, as the metropolitan Shemon Bar Qaligh of Tangut was arrested by the patriarch Denha I shortly before his death in 1281 'together with a number of his bishops'. The province of Katai (Cathay) and Ong, which seems to have replaced the old Tang dynasty province of Beth Sinaye, covered northern China and the country of the Christian Ongut tribe around the great bend of the Yellow River. The metropolitans of Katai and Ong probably sat at the Yuan capital Khanbaliq. The patriarch Yahballaha III grew up in a monastery in northern China in the 1270s, and the metropolitans Giwargis and Nestoris are mentioned in his biography. Yahballaha himself was consecrated metropolitan of Katai and Ong by the patriarch Denha I shortly before his death in 1281. During the first half of the 14th century there were Church of the East Christian communities in many cities in China, and the province of Katai and Ong probably had several suffragan dioceses. In 1253 William of Rubruck mentioned a Church of the East bishop in the town of 'Segin' (Xijing, modern Datong in