The Lotharian legend was a German 16th-century theory which purported to explain why Roman law as outlined in the Byzantine was the law of the Holy Roman Empire (as the). According to this theory – which was conclusively disproven by Hermann Conring in 1643 – the Holy Roman Emperor Lothair III had commanded in 1137 that Roman law was the law of his empire.
Today, the German Lutheran reformer and theologian Philip Melanchthon is acknowledged as the creator of this legend.
Long after the Western Roman Empire had fallen, the, a 6th-century legal collection of Eastern Roman emperor Justinian I, was the law of the land in vast parts of Europe (as the). Due to the lack of a tangible explanation why the was the applicable law, different theories were developed during the Late Middle Ages and the beginning of the early modern period to justify its use.
One theory argued with the inherent (reason and equity) of Roman law and its inherent spiritual authority. Especially with a view to the Holy Roman Empire, another theory focused on the idea of : According to this concept, the imperial authority of the ancient Roman emperors had been passed on to the Holy Roman emperors. As the purported successors of the Roman emperors, the Holy Roman emperors also carried with them the ancient Roman law.
The Lotharian legend was a further theory to justify the usage of Roman law. Its backdrop formed the second campaign of Lothair III in Italy in 1137. It explained the application of Roman law in the German territories by virtue of a decree by emperor Lothair III.
Johann Carion, the court astrologer to the prince-elector of Brandenburg, Joachim I Nestor, espoused in his 1532 treatise, the, the view that Emperor Lothair III had commanded the teaching of Roman law in his empire and its application in his courts after Irnerius had rediscovered the in the 12th century.
The authorship of the is, however, disputed and today the German Lutheran reformer and theologian Philip Melanchthon is considered to be the author of at least parts of it. For the part containing the Lotharian legend, his authorship is clearly established. The textual origin of this idea of Melanchthon remains, nevertheless, unclear. Legal historian considered the possibility that the of Burchard of Ursperg could be its origin because Ursperg's discussion of Irnerius also notes Irnerius' patroness Matilda of Tuscany, but he concedes that this is inconclusive, because the does not contain any reference to the alleged imperial decree of Lothair III. Alan Watson simply notes that the legend "was apparently the invention of Phillip Melancthon".
Considering the motives of Melanchthon, legal scholar argues that theological reflections were decisive for Melanchthon's espousal of the Lotharian legend. For Melanchthon, God wanted laws to govern his people. This law had to be revealed in authoritative texts as it was the case with the Ten Commandments. Customary law as a method of explaining the applicability of the did not provide the legal certainty which Melanchthon deemed necessary and could not guarantee that the would be applied in total .
Legal scholar remarked that the Lotharian legend was a "political myth" and was not discussed in contemporary legal circles and was thus a project of political legitimization and not a legal argument. He highlights that the legal commentators of the time apparently did not question the applicability of Roman law; for them the applicability of the was self-evident and they pragmatically just applied it.
Hermann Conring was not the first scholar who attempted to disprove the Lotharian legend. It was refuted earlier by in his chronicle of Speyer (1612). called it a "fantasy" in 1613 and Georg Calixtus criticized it extensively in his 1619 .
But the legend was only conclusively disproven by Hermann Conring in chapters 20 and 21 of his 1632 opus magnum (On the origin of German law). Conring argued that no earlier document existed that contained a trace of the decree of Lothair III. He thus concluded that purported historical events should only be considered to be established as true if they were attested to by credible and near-contemporaneous sources.
In lieu of an imperial decree Conring's explanation for the applicability of Roman law was that it had been gradually adopted by the courts without a clear commandment to do so. Conring thereby established the modern consensus view of a gradual reception of the focusing on the fact that in legal education only Roman law was taught and thus trained lawyers had a natural inclination to apply it.