The Liber Pergaminus by Moses del Brolo is certainly more than a laudatory description of the city. Foundation myths and exempla taken from Roman history are interwoven with an exaltation of the present time that has traditionally been read as a propagandistic support of the episcopate of Ambrogio Mozzi (1111/2-33). However, many of the points on which the last editor, Guglielmo Gorni, had drawn attention, implicitly soliciting further study, remain in the shadows: the reference is to the concrete and immediate occasions of the elaboration of the text of Moses, to its recipients and all the reades actually capable of decoding the language and contents of the proposal, of unravelling the thread that weaved a dense web of allusions, analogies, silences and removals. Reconstructing the gestation context of the Liber Pergaminus – and offering new reflections for a more stringent dating of the work –, the contribution intends to deal with these problems by showing the coherent design of the rhetoric of Moses, his industrious declination in the midst of the political conflict and in various connections with all the actors on the stage.