Concordat of Worms
Shortly after gaining office, he began construction of the castle of Volmarstein. Frederick took part in drawing up the Concordat of Worms which ended the Investiture Controversy in 1122. Frederick elected Lothair of Saxony over Duke Frederick II of Swabia in 1125, after first offering the crown of Germany to Charles I the Good of Flanders. King Lothar secured the south of the archbishopric through the construction of a series of castles.