This article deals with the problem of the imperial intervention of the emperor Constantine in Church matters and proposes a reconsideration of the active measures that he takes to favour the Christian Church. The paper presents a wider scope of the sources: on the one hand it re-examines the Christian ones, but above all, it adds others that, although they are temporally further away from Constantine, give a more complete approach of the role of the Roman emperor as head of the Empire and the specific functions he had to fulfil as pontifex maximus. The first part of the article covers the personal and institutional background of the emperor -that will help to situate him in his particular circumstances- and the second one re-evaluates specific and paradigmatic examples of the problem under consideration.