‘Governing the world by writing’ is the intriguing title of a recent book about the late antique and medieval papacy. The subtitle reveals it to be about relations with Dalmatia only,1 but the concept is applicable to the present work, which tries to explain how the papacy governed the world, in its religious aspects at least, by means of documents. The ‘power’ with which the book is concerned is ‘power to’ more than ‘power over’.2 ‘Protocol’ in the title is understood in a sense transferred from the world of computing as ‘A (usually standardised) set of rules governing the exchange of data’ (Oxford English Dictionary). The implicit analogy with software is not inappropriate, since an argument running through the book will be that cleverly designed systems compensated for the inadequacies of the ‘hardware’ of papal government – for its lack of a properly financed bureaucratic infrastructure.