After the death of his father at the 982 Battle of Stilo, his elder brother was enfeoffed with the Margraviate of Meissen by King Otto III.
In 1002, following Eckard's failed attempt at the throne in the German royal election and his subsequent assassination, Bolesław occupied Meissen, but the new king, Henry II forced him to leave it and accept the March of Lusatia with the adjacent Milceni lands instead.
The Church, however, largely opposed the slave trade: Thietmar railed against the "barbaric" practice the Saxons had shown of dividing up families in order to sell them.
[3] The margrave had travelled to Merseburg for a Fürstentag, where on June 5 he was arrested and handed over to the safekeeping of Bishop Arnulf of Halberstadt.
His margraviate was bestowed on his nephew Herman; while Gunzelin himself was imprisoned for eight years in the farming village of Ströbeck near Drübeck Abbey in the Saxon Harzgau.