Walk to Canossa
In February 1076 Pope Gregory VII had excommunicated Henry over the Investiture Controversy. In turn, the rebellious German princes met at Trebur in October and resolved upon his deposition, if he would not be able to obtain the revocation of the ban within a year. By his Walk to Canossa in January 1077, the king received absolution, nevertheless the princes elected Rudolf of Rheinfelden anti-king on March 15.