Rus is by the Muslim diplomat and traveller Ahmad ibn Fadlan, who visited Volga Bulgaria in 922, and described people under the label Rūs/Rūsiyyah at length, beginning thus: Apart from Ibn Fadlan's account, scholars draw heavily on the evidence of the Persian traveler Ibn Rustah who, it is postulated, visited Novgorod (or Tmutarakan, according to George Vernadsky) and described how the Rus exploited the Slavs. Byzantine sources When the Varangians first appeared in Constantinople (the Paphlagonian expedition of the Rusʹ in the 820s and the Siege of Constantinople in 860), the Byzantines seem to have perceived these people they called the Rhos () as a different people from the Slavs. At least no source says they are part of the Slavic race. Characteristically, Pseudo-Simeon and Theophanes Continuatus refer to the Rhos as dromitai (Δρομῖται), a word related to the Greek word meaning a run, suggesting the mobility of their movement by waterways. In his treatise De Administrando Imperio, Constantine VII describes the Rhos as the neighbours of Pechenegs who buy from the latter cows, horses, and sheep "because none of these animals may be found in Rhosia". His description represents the Rus as a warlike northern tribe. Constantine also enumerates the names of the Dnieper cataracts in both rhosisti ('ῥωσιστί', the language of the Rus) and sklavisti ('σκλαβιστί', the language of the Slavs). The Rus names are usually etymologised as Old Norse. An argument used to support this view is that the name Aeifor in reference to the fourth cataract is also attested on the Pilgårds runestone from the 10th c. on Gotland. However, some researches indicate that at least several of the Rus names can be Slavic and, as for the Dnieper cataract Aeifar / Aeifor, its name doesn't have an acceptable and convincing Scandinavian etymology. {| class="wikitable" |+ !Constantine's form for the non-Slavonic names !Latin transliteration !Constantine's interpretation of the Slavonic or both !Proposed Old Norse etymons for the non-Slavonic names !Proposed Slavic etymons for the non-Slavonic names |- |Ἐσσουπῆ |Essoupi |"Do not sleep!" |nes uppi "upper promontory" súpandi "slurping" |не спи (ne spy) "do not sleep!" (compare the Ukrainian не спи /ne spɪ/ "do not sleep!") |- |Οὐλβορσί |Oulvorsi |"the Island of the Barrage" |Úlfarsey "Úlfar's island" hólm-foss "island rapid" |— |- |Γελανδρί |Gelandri |"Noise of the Barrage" |gjallandi/gellandi "yelling, loudly ringing" |— |- |Ἀειφάρ, Ἀειφόρ |Aeifar, Aeifor |... because the pelicans nest in the stones of