This research is framed within a broader line in which the author addresses the reciprocal relations between Art and Architecture of the twentieth and twenty-first centuries. Thus, the essential figure of Álvaro Siza, architect and artist, is analysed in relation to the role of drawing in his process of artistic-architectural ideation. The aim is to clarify, not only the genius of his production, but above all and especially his role as a catalyst and defender of a total art, undoubtedly charged with mysticism. In this sense, his integrative conception of art makes it possible to see the richness of his thought, which is expressed through a 'hand that knows', that is, wise, human and divine at the same time.