Dissertatio de corona ferrea Langobardorum.

A description of the iron crown of Lombardy, which is both a holy relic and one of the oldest royal insignia of Christendom. Itwas made in the Early Middle Ages and is so called because it was believed to contain a centimeter-wide band of iron within it, said to be beaten out of a nail of the True Cross. In some accounts, the crown was used in Charlemagne's coronation as King of the Lombards.