Sentence:  Geographers and historians have been sadly puzzled where to find its site; and some, as Malte Brun, have supposed it to have been merely a summer abode of the <WSD>Karait</WSD> and Mongolian Khans, like that of Zheholl, where the emperor or khan long received the British embassy. 
Meaning of the word marked with <WSD> tags:  (Karaite) (member of a particular Turco-Mongol tribal confederation)