Otto's army descended into northern Italy in August 961 through the Brenner Pass at Trento. The German king moved towards Pavia, the former Lombard capital of Italy, where he celebrated Christmas and assumed the title King of Italy for himself. Berengar II's armies retreated to their strongholds in order to avoid battle with Otto, allowing him to advance southward unopposed. Otto reached Rome on 31 January 962; three days later, he was crowned Emperor by Pope John XII at Old St. Peter's Basilica. The Pope also anointed Otto's wife Adelaide of Italy, who had accompanied Otto on his Italian campaign, as empress. With Otto's coronation as emperor, the Kingdom of Germany and the Kingdom of Italy were unified into a common realm, later called the Holy Roman Empire.