THE relation between the regnum and the sacerdotium in the eleventh and twelfth centuries has attracted the attention of many generations of distinguished scholars, and with the publication of Ulhnann's The Growth of Papal Government in the Middle Ages, initerest bids fair to continue. Those interested in this problem, as well as all those concerned with the history of the Papacy in the Middle Ages, should be greatly stimulated by the wealth of material now available to us concerning the Latin kingdom of Jerusalem. For surely it is not without significance as to how the two powers were related in that kingdom established by the First Crusade. Indeed, the great historians of the crusade -La Monte, Munro, Rohricht, Runciman, and others, including the authors of the new American crusade history' sponsored by the Mediaeval Academy of America have not only provided us with the material; they have also attempted to answer the problem, if only in passing. Perhaps there is some justification in investigating the papal attempt to establish a proper relationship between the regnum and the sacerdotium in Jerusalem. Certainly, such an investigation would cast additional light on the great aims pursued by the post-Hildebrandine Papacy. In the contest between the regnum and the sacerdotium, the reign of Paschal II is of great importance, both in the West and in the Latin Orient. At the outset of his reign, Paschal stood in the tradition of Gregory and Urban, who had labored for the emancipation of the Church from the temporal power. Insisting upon the pre-eminence of the sacerdotium, they demanded as a consequence the withdrawal of the temporal power from all interference in the disposition of ecclesiastical benefices and offices. Lay investiture, either in regard to the spiritualia or the temporalia of an ecclesiastical office, was repeatedly forbidden. The violent conflicts engendered by the papal decrees we call the Investiture Controversy. However, in the reign of Paschal II there was a considerable advance towards a creative solution. Under the leadership of such men as Ivo of Chartres, the Latin Church in the West began to distinguish more sharply between the spiritual and temporal functions of an ecclesiastical office, particularly in regard to the episcopate. While the Church continued to forbid lay interference in episcopal elections and lay investiture of the spiritualia of an ecclesiastical office, the Church was now prepared to grant to the temporal power the right to invest a bishop, canonically elected and consecrated, with the temporalia of his see. The Concordat of Worms, five years after Paschal's death, marks the coming of age of this new pattern in the relationship between the spiritual and temporal powers. The new pattern related the two powers in such a way that, while each would preserve its own rights and freedom in its own proper sphere of action, the two powers would be