Hidden as it is amongst the magnificence of the ancient ruins and the splendour of the Renaissance palazzos, the squares and Baroque churches, Medieval Rome seems to shy away from the observer’s gaze. Once capital of a vast empire, the beating heart of civilisation and power, during the Middle Ages Rome lost, together with its role of sole and uncontested world power, the strength and beauty that were its distinctive traits. In the power vacuum that followed the collapse of the Empire, the papacy asserted itself as the new ideological and political point of reference and Rome becomes the capital of Christianity. In the account by leading historians, it was this boom and bust cycle that carved out the distinctive features of Medieval Rome: the excessive power of the aristocracy and its in-fighting, its demographic and urban expansion, its first jubilee in the fourteenth century, its decline culminating in the transfer of the papal seat to Avignon and finally, the return of the papacy, destined to transform the Eternal City into the theatre of its ambitions.