In his Defensio fidei catholicae de satisfactione Christi adversus Faustum Socinum Senensem Grotius makes use of sources taken from Roman law. We discuss three examples and ask the question whether something may be said about the weight of the arguments Grotius has taken from Roman law, mainly the Digest. The first one relates to his belief that it is a matter of public interest that crimes do not remain unpunished and he calls this argument even a trivial commonplace: Hoc enim iudicare videtur trita sententia delicta puniri publice interest. (2) The second example is Grotius’s thesis that si alio animo alius idem solvat, liberatio non contingit. (3) The third example is his thesis that ex Romanorum legibus … poenae variantur pro conditione personarum which he also justifies with an impressive number of references. The conclusion is that Grotius uses these arguments, as if they were propositions suitable to function as part of the theological construction apt to rebut the views of Socinus, but for that purpose Grotius´s quotations are generally taken out of their original context and landed on a sort of Procrustean bed of his theological presuppositions.