Throughout China’s imperial history there have been numerous attempts to establish dynasties, of which a considerable number resulted in ‘marginal dynasties’, that are short-lived and locally confined rules. These have been deemed illegitimate by traditional Chinese historiography, even though they naturally considered themselves as legitimate. Taking the example of the Great Xia this paper describes in detail their rise and fall and examines, how this ‘marginal dynasty’ claimed legitimacy. By contrasting evidence for traditional patterns of legitimation and elements of radical millenarian beliefs, it will be shown that, although the Xia's origins lay in a religiously motivated uprising and these beliefs continued to be vital, its leaders eventually turned to the established tradition and their representatives, former officials and scholars, in order to secure legitimacy.