The Lotharian Legend is an early modern theory that explained the validity of Roman law (Ius commune) in Germany. It claimed that, in 1137, Emperor Lothair III of Supplinburg had decreed by law that Roman law was applicable in the Holy Roman Empire.

The Lotharian Legend emerged against the background of questions by late medieval and early modern jurists as to why Justinian’s Corpus Iuris Civilis, the great sixth-century codification of ancient (late antique) Roman law created in the eastern Roman Empire was still regarded as valid law in large parts of Europ…