ruined 10th-century castle southwest of Reggio nell'Emilia in Italy, famous as the meeting place (1077) of Pope Gregory VII (Gregory VII, Saint) and Emperor Henry IV. The stronghold was built c. 940 by Atto Adalbert, the founder of the House of Attoni and first count of Canossa.

At the invitation of Matilda (Matilda of Canossa), countess of Canossa (Matilda of Tuscany), a strong supporter of the papacy in the Investiture Controversy, Gregory VII stayed at the fortress in 1077 while on his way to Germany to take action against his opponent, Henry IV. To forestall his deposition, Henry journeyed to Canossa as a simple penitent and, on January 28, after waiting for three days, received absolution.

Though this did not mark any lasting victory for the papacy, the name Canossa became associated with the submission of the secular power to the church; hence Bismarck's dictum, during Prussia's Kulturkampf against Roman Catholic influences in Germany: “Nach Canossa gehen wir nicht” (“We are not going to Canossa”).

The castle was destroyed in 1255 by the people of Reggio.