Basil I, in which Basil (in a letter now lost) appears to have claimed that chaganus is a title used amongst the Avars, Khazars and Normans; Louis replies he has heard of a Avar caganum, but never of Khazar or Norman ones: "But we have found that the leader (praelatus) of the Avars is called Khagan (chaganum), but not (non) the leader of the Gazani or the Northmen..." ("Chaganum vera nos praelatum Avarum, non Gazanorum aut Nortmannorum nuncupari repperimus …"). (1c) The Arabic "Anonymous Note" dating from 870–880, which was reused by a number of Arabic and Persian writers, including the following: Ahmad ibn Rustah wrote 903–913 (or 920) in an Arabic-language book that the Rus' had a prince called khāqān rus or Khaqan-Rus. Hudud al-'Alam (anonymous late-10th-century Persian-language geography text) refers to the Rus' king as "Khāqān-i Rus". Abu Saʿīd Gardīzī ((died 1061), Zayn al-Akhbār (11th century), also referred to "Khāqān-i Rus". (2a) Hilarion of Kiev's 11th-century Sermon on Law and Grace mentions the title of kagan five times, and applies it to Volodimir I (Vladimir/Volodymyr "the Great" ), and his son Georgij, baptismal name of Yaroslav the Wise (). (2b) A short inscription on the wall of Saint Sophia Cathedral, Kyiv expresses a plea for divine deliverance for the (unnamed) "our kagan", possibly prince Sviatoslav II of Kiev (). (2c) The Tale of Igor's Campaign (12th century) calls Oleg I of Chernigov a kogan. According to Ostrowski (2018), 'the word kogan is referring to a specific ruler or just to a time when then were khagans.' Annales Bertiniani sub anno 839 The earliest claimed reference related to Rus' people ruled by a "khagan" comes from the Frankish Latin Annales Bertiniani, which refer to a group of Norsemen who called themselves Rhos () and visited Constantinople, capital of the Byzantine Empire, around 839. Fearful of returning home via the steppes, which would leave them vulnerable to attacks by the Magyars, these Rhos travelled through the Frankish kingdom accompanied by Byzantine Greek ambassadors from the Byzantine Emperor Theophilus. When questioned by the Frankish king Louis the Pious at Ingelheim, they stated that their leader was known as chacanus (hypothesized to be either the Latin word for "khagan" or a deformation of Scandinavian proper name Håkan), that they lived far to the north, and that they were Swedes (comperit eos gentis esse sueonum). Chronicon Salernitanum Thirty years later, in spring 871,