 The Pannonian Avars were also known by names including "Uarkhon" or "Varchonites" – which may have been portmanteau words combining "Var" and "Chunni".The 18th-century historian Joseph de Guignes postulated a link between the Avars of European history with the Rouran Khaganate of Inner Asia based on a coincidence between Tardan Khan's letter to Constantinople and events recorded in Chinese sources, notably the "Wei Shu" and "Bei Shi".Chinese sources state that Bumin Qaghan, founder of the First Turkic Khaganate, defeated the Rouran, some of whom fled and joined the Western Wei.