The chief task of the bishops of the new see was the conversion of the Wends, to which Bishops Volkold (died 992) and Eido (died 1015) devoted themselves with great zeal; but the slow evangelization was yet incomplete when the investiture conflict threatened to arrest it effectively. Saint Benno (1066–1106), bishop when these troubles were most serious, was appointed by Henry IV and appears to have been in complete accord with the emperor until 1076; in that year, although he had taken no part in the Great Saxon Revolt, he was imprisoned by Henry for nine months. Escaping, he joined the Saxon princes, espoused the cause of Pope Gregory VII, and in 1085 took part in the Gregorian Synod of Quedlinburg, for which he was deprived of his office by the emperor, a more imperially disposed bishop being appointed in his place. On the death of Gregory, Benno made peace with Henry, was reappointed to his former see in 1086, and devoted himself entirely to missionary work among the Slavs.