gradually waned until 994 when Otto III reached the age of 14. At an assembly of the Imperial Diet held in Solingen in September 994, Otto III was granted the ability to fully govern the kingdom without the need of a regent. With this, Adelaide retired to a nunnery she had founded at Selz in Alsace. Although she never became a nun, she spent the rest of her days there in the service of the Church and in acts of charity. As Otto III was still unmarried, from 995 until 997 his older sister Sophia accompanied him and acted as his consort. One of Otto III's first actions as an independent ruler was to appoint Heribert of Cologne as his chancellor over Italy, a position he would hold until Otto's death in 1002. Otto III followed in his grandfather Otto I's footsteps in the beginning of his reign, by appointing a new pope, Gregory V, and leaving Rome. Gregory V was expelled and Otto III returned to Rome in 998 where he stayed permanently until his death. In the summer of 995, Otto sent the Archbishop of Piacenza, John Philagathos, to Constantinople as his representative to arrange a marriage between himself and a Byzantine princess following the example of his father, Otto II, who solidified his claim to the throne by marrying the Byzantine Theophanu. For a while the discussions were about Zoe Porphyrogenita. War against the Slavs The Lutici federation of West Slavic Polabian tribes had remained quiet during the early years of Otto III's reign, even during Henry II's failed rebellion. In 983, following Otto II's defeat at the battle of Stilo, the Slavs revolted against Imperial control, forcing the Empire to abandon its territories east of the Elbe River in the Northern March and the Billung March. With the process of Christianization halted, the Slavs left the Empire in peace, and with Henry II's rebellion put down, Theophanu launched multiple campaigns to re-conquer the lost eastern territories, beginning in 985. Even though he was only six at the time, Otto III personally participated in these campaigns. During the expedition of 986 against the Slavs, Otto III received the homage of Duke Mieszko I of Poland, who provided the Imperial army with military assistance and gave Otto III a camel. Although the Lutici were subdued for a time in 987, they continued to occupy the young king's attention.