Bucer's efforts to reform the church in Wissembourg resulted in his excommunication from the Roman Catholic Church, and he was forced to flee to Strasbourg. There he joined a team of reformers which included Matthew Zell, Wolfgang Capito and Caspar Hedio. He acted as a mediator between the two leading reformers, Martin Luther and Huldrych Zwingli, who differed on the doctrine of the eucharist. Later, Bucer sought agreement on common articles of faith such as the Tetrapolitan Confession and the Wittenberg Concord, working closely with Philipp Melanchthon on the latter.