Zwingli's closing years were devoted to vast schemes of European policy. With the view of forming a strong alliance of the Swiss Protestants with foreign powers favouring the reformed faith, and in opposition to the emperor Charles V., he entered into negotiations with France, with some of the German states, with the Venetian republic, and others. His plans were too bold and sweeping to be practical, and came to nought. His relations with Luther claim special attention, however. By his treatise, "De verâ et falsâ religione" (1525), Zwingli had, though unwillingly, thrown the gauntlet into the Wittenberg camp. The work was intended to be a scientific refutation of the Catholic doctrine of transubstantiation, and a war of words arose. The contest was by each disputant carried on _suo more_ by Luther with his usual authoritative and tempestuous vehemence, by Zwingli in his own cool reasoning, dignified, and courteous style and republican frankness. Presently there came a strong desire for a union between the German _Protestants_, and the Swiss _Reformers_--the two were thus distinguished--the impulse to it being given by Charles V.'s "Protest" against the Protestants. Landgrave Philip of Hesse, the political leader of the German reformers, invited Luther and Zwingli to meet at his castle of Marburg, with the view of reconciling the two sections. The religious _colloquium_ was attended by many savants, princes, nobles, and all the chief leaders of the Reformation, and might have done great things, but came to grief through the obstinacy of Luther, as is well known, or rather through his determination to approve of no man's views except they should agree exactly with his own. Luther insisted on a literal interpretation of the words "This is my body," whilst Zwingli saw in them only a metaphorical or symbolical signification. Zwingli's logic and cool, clear reasoning were acknowledged to be superior to those of his opponent, but Luther demanded complete submission. The conference, in short, resulted in nothing, and nearly ended in an open rupture between the two leaders. Zwingli extended his hand in token of friendship and goodwill, but Luther refused it. The truth was the two men looked at the matter from quite different points of view. With Luther religion was almost wholly a thing of a mystic basis, a creed of the heart--of feeling--whilst Zwingli, required his reason to be satisfied. The one wrestled in agony of soul with the spirits of darkness; the other looked to the Divine, all-embracing love under which all creation rests in trust and happiness, and under which all men are brothers, children of one all-kind Father.