Thietmar of Merseburg
For the "Monumenta Germaniae historica" he edited the "Chronicon" of Thietmar of Merseburg, the "Gesta Hammenburgensis ecclesiae pontificum" of Adam of Bremen and the "Chronica Slavorum" of Helmold, with its continuation by Arnold of Lübeck. Lappenberg, who was a member of numerous learned societies in Europe, wrote many other historical works.