The papal legate, Cardinal Bernard, excommunicated Henry on 12 November 1077. Henry sent Bishops Benno II of Osnabrück and Theoderic of Verdun to Rome to begin negotiations with the Pope, whose position in Italy had been weakening. The Pope appointed a new legate, whose name was not recorded, to represent him in Germany. The papal legate celebrated Easter with Henry in Cologne on 8 April 1078, demonstrating that the Pope had not regarded Henry's excommunication as valid. Henry invaded Lotharingia and forced Bishop Herman of Metz into exile, but Berthold of Zähringen and Welf of Bavaria inflicted defeats on his Swabian and Franconian supporters. Rudolf of Rheinfelden hurried to Franconia and met Henry and his army of 12,000 Franconian peasants at Mellrichstadt on 7 August. The Battle of Mellrichstadt proved indecisive.
