Enrique III el Negro
However, Casimir I in 1039 was supported by Henry III, Holy Roman Emperor against the Bohemians and soon afterwards he also concluded an alliance with Kievan Rus. This allowed him to gather enough forces to subdue Miecław. In 1047 he was attacked by the joint forces of Casimir I and Yaroslav I the Wise and was probably killed in a battle on the banks of Vistula.