Before rediscovering the corpus aristotelicum, the clergy of the Middle Ages elaborated the definitions of lex and iustitia making use of the ancient sources of Roman law in the Justinianean Books the Digest and the Institutions) and the various Decretals of pontifical law organised in the Decretum of Gratianus.

In that context, the law emphasised the political aspect above all, both in its genesis on the part of a public authority and in its finalisation for the public good, and that most strictly juridical of its vis coërcitiva.

Through the most famous medieval encyclopaedist, Isidor of Seville, they then recovered the stoic notion of lex naturalis, exalted by Cicero as the base and measure of any ius conditum and condendum.

In addition, they appropriated the deep Augustinian meditation of lex aeterna as a rational archetype and normative principle aimed at achieving order and peace for the whole universe created with the destiny of human history.

Following Augustine, the essence of justice was identified in the constant willingness of the soul to give everyone that which was due them: to God, to one's neighbour, to oneself, keeping in mind the good of the community and conforming oneself to the divine plan in the creation of the world and to its providence for the history of man.

These texts were familiar to the pre-Scholastic theologians. From the recent research of Francisco da Gama Caeiro and his students, we know today that these were also present in the libraries of the Canons of Lisbon and Coimbra, where Saint Anthony studied and received his training.