Between the 13th and 14th centuries Europe was the scene of profound socio-cultural transformations. The decline of the centres of power that had governed the continent for the last three centuries - the Empire and the Papacy - was matched by the emergence of new national realities, above all the Kingdom of France. A change in power relations made evident by a paradigmatic event such as the Avignon Captivity (1309) and even more so, within the limits of folklore, by the Slap of Anagni (1303). Medieval universalism, which had thus entered a crisis, opened the way for new forms of particularism in the institutional and legal spheres. The systematisation of knowledge carried out in these areas in the 13th century though influential, would become the subject of profound rethinking as early as the following century. The theological foundations of law and sovereignty in particular will be called into question. This process, multiform and not easy to read, finds a forerunner in Aegidius Romanus (c. 1243-1316), an Augustinian, a probable pupil of Aquinas, archbishop of Bourges (1295) and an undisputed protagonist of the institutional events that marked the turn of the century. Between 1277 and 1280 he wrote De regimine principum whose tutor he may have been. Here the author, starting from Aristotelian and Thomist premises, rethinks the relationship between law and sovereignty, strongly emphasising the role of the prince as implementer of natural law and dominus of positive law, thus anticipating future voluntarist tendencies. In 1302 he published De Ecclesiastica potestate (1302), which places him among the greatest theorists of papal plenitudo potestatis. These texts, like those of other 'borderline' authors, reread from a historical-legal perspective, allow the contradictions and intellectual ferment that characterised this season of late medieval thought to emerge, behind which one can already discern the modernity