This paper examines the intellectual and religious debates involved in the action of the Fourth Lateran Council in condemning the criticism made by Joachim of Fiore of Peter Lombard's understanding of the Trinity. The authors argue that this condemnation, of decisive influence in shaping the direction of scholastic theology in the 13(th) century, marks the victory of one particular school of thought being developed in Paris in the second half of the 12(th) century, that of Peter Lombard, as well of his particular way of understanding God as summa quaedam res, conceptually distinct from the three divine persons, even if they shared in the same divine nature. While Lombard was inspired by a phrase of Augustine's De doctrina Christiana, he subtly rephrased Augustine's argument in a way that was seen by Richard of St. Victor as creating unnecessary separation between the divine persons and the dynamic nature of God as love that flowed into the divine persons. The authors argue that Joachim's objection to Lombard's analysis was inspired by Richard of St. Victor's own critique of Lombard's understanding of the Trinity, distinct from and perhaps more cogent than the accusations made about Lombard's Christology by his critics, many of whom were connected in some way to St. Victor. The official support given to Peter Lombard at Lateran IV was intimately connected to the desire of Innocent III and his senior advisers to create an unchallenged foundation for theological orthodoxy at the newly established University of Paris.