The Humiliation of Canossa, (Italian: L’umiliazione di Canossa), sometimes called the Walk to Canossa (German: Gang nach Canossa/Kanossa) or the Road to Canossa, was the ritual submission of the Holy Roman Emperor, Henry IV to Pope Gregory VII at Canossa Castle in 1077 during the Investiture controversy. It involved the Emperor journeying to Canossa, where the Pope had been staying as the guest of Margravine Matilda of Tuscany, to seek absolution and the revocation of his excommunication.
According to contemporary sources, he was forced to supplicate himself on his knees waiting for three days and three nights before the entrance gate of the castle, while a blizzard raged. Indeed, the episode has been described as “one of the most dramatic moments of the Middle Ages“. It has also spurred much debate among medieval chroniclers as well as modern historians, who argue about whether the walk was a “brilliant masterstroke” or a humiliation. (Source)