Kiev at the time and was Hilarion's patron. A colophon preserved in a 15th-century manuscript, at the end of a set of works usually attributed to Hilarion, adds one more mention: Быша же си въ лѣто 6559 (1051), владычествующу благовѣрьному кагану Ярославу, сыну Владимирю. Аминь. ("These things came to pass in the year 6559 (1051), during the reign of the pious kagan Jaroslav, the son to Volodimer, Amen.") Absence in other contemporary sources The absence of any khagan in the following sources has been taken by several scholars as evidence indicating either that there had never been a Rus' khaganate (Tolochko 2015, Ostrowski 2018), or that it must have disappeared by 911 (Zuckerman 2000), probably already before 900 (Golden 1982). The Book of Roads and Kingdoms ( 870) written by Persian geographer Ibn Khordadbeh does mention the Rus' as important traders, but does not mention a title of a Rus' ruler in his chapter "Titles of the rulers of the Earth", where only the Turks, Tibetans and Khazars are said to be ruled by khaqans. If the Rus' had a khaqan at the time, the author would have been expected to mention it, but he did not. Ibn Khordadbeh's book is a notable exception amongst the Arabic-Persian sources in mentioning the Rus', but not a khaqan; more generally, his information also does not appear to stem from the same source (possibly the now-lost book written by Jayhani) used by others such as Ibn Rusta and Gardizi. The Primary Chronicle (an anonymous Rus' chronicle completed 1110) does not mention the title of khagan anywhere, for example in the three Rus'-Byzantine treaties of 907, 911, and 944. The Risala of Ahmad ibn Fadlan (written in Arabic, documenting his visit to Kievan Rus' around 922) calls the monarch of the Rus' a malik (Arabic for "king"), not a qagan, even though it does say that 'the king of the Khazars [is] called a Qagan'. De Ceremoniis (a Greek book on ceremonial protocol at the Byzantine court from the 950s) meticulously documents the titles of foreign rulers, but when it deals with Olga of Kiev's reception at the court Constantine VII in 945, it does not call her a khagan, but an archon (Greek for "ruler"). Dating The dating of the Khaganate's existence has been the subject of debates among scholars and remains unclear. Paul Robert Magocsi and Omeljan Pritsak date the foundation of