 From 1015, he also appeared as a and count in the neighbouring Schwabengau.Upon the death of his uncle Frederick I, who had died without male issue in 1017, he inherited Eilenburg and Brehna.In 1018, Theodoric and his brother-in-law, Margrave Herman I of Meissen acted as witnesses when the Peace of Bautzen was concluded between Emperor Henry II and the Polish ruler Bolesław I the Brave, ending a lengthy German–Polish War.