Walk to Canossa
From the outset, Urban had to reckon with the presence of Guibert, the former bishop of Ravenna who held Rome as the antipope "Clement III". Gregory had repeatedly clashed with the emperor Henry IV over papal authority. Despite the Walk to Canossa, Gregory had backed the rebel Duke of Swabia and again excommunicated the emperor. Henry finally took Rome in 1084 and installed Clement III in his place.