Luther’s description of the Marburg colloquy (1529), in a letter to his wife, Katherina.

Know that our amicable conference at Marburg is now at an end and that we are almost in agreement on all points except that our opponents maintain that there is mere bread and wine in the Lord's Supper, and that Christ is only present in a spiritual sense. Today the landgrave intervened to bring us to agreement, hoping that although we disagreed we would still regard each other as brothers and members of Christ. He tried hard, but we would not call them brothers or members of Christ although we wish them well and desire to remain at peace . . . Tell Bugenhagen that Zwingli's best argument was that a body could not exist without occupying space and therefore Christ's body was not in the bread, and that Oecolampadius' best argument was that the Sacrament is only the sign of Christ's body. I think God blinded them so that they could not get beyond these points.

Zwingli’s description of the same meeting, in a letter to his colleague Vadian.

I'll give you a brief account of what you are so anxious to learn . . . Luther, Melanchthon, Oecolampadius and Zwingli entered the arena in the presence of the landgrave and a few others, twenty-four at most. We fought it out . . . before witnesses to a winning battle over four sessions in all. Three times we threw at Luther the fact that he had at other times given a different exposition from the one he was now upholding, those ludicrous ideas of his that Christ suffered in his divine nature, that the body of Christ is everywhere, and that the flesh profits nothing. But that fine fellow had nothing at all to say in reply, except that on the matter of the flesh profiting nothing he said: 'You know, Zwingli, that all the ancient writers have time and again changed their interpretation of passages of Scripture as time went on and their judgement matured.' He said: 'The body of Christ is eaten and received into our body in the bodily sense, but at the same time I reserve my judgement on whether the human spirit eats his body too.' But a little before he had said: 'The body of Christ is eaten by the mouth in the bodily sense, but the human spirit does not eat him in the bodily sense.' He said: 'The body of Christ is constituted by saying the words "This is my body", however great a criminal the person saying them might be.' He conceded that the body of Christ is finite. He conceded that the Eucharist might be called a sign of the body of Christ.

These are examples of the countless inconsistencies, the absurdities and stupidities which he bleats out like a babbling brook. But we refuted him so successfully that the landgrave himself now agrees with us, although he conceals it before the other princes. The Hessian party has almost all abandoned Luther's position. The landgrave himself has given permission for our books to be read with impunity and in future will not allow bishops who share our views to be removed from office.

We left Marburg with certain agreements which you will soon see in writing. The truth prevailed so manifestly that if ever a man was beaten it was Luther - for all his impudence and obstinacy - and everyone witnessed it too, although of course the judge was discreet and impartial. Even so, Luther kept protesting that he had not been beaten. However, we have achieved this much good, that our agreement on the rest of the doctrines of the Christian religion will preclude the papal party from hoping any longer that Luther will come over to them.