Arthur Koestler's book is dedicated to the history of the birth, heyday and mysterious disappearance of the powerful Khazar state from the map of Eurasia. Based on numerous Arabic, Byzantine and Old Russian sources, attracting the works of Artamonov, Kokovtsov, Toynbee, Vernadsky, Dunlop, Kuchera, Polyak and other historians, the author offers his original vision of the formation and collapse of the Khazar Khaganate.