Sir W. Martin Conway said:
There is also the ninth century so-called Iron crown at Monza, which may give us some idea of what Charlemagne's crown may have been like. The Iron crown probably belonged to Berengar and was made to be worn. It consists of six curved gold plates hinged together, and the only use of the hinging must have been to enable the circlet to fit a human head. The iron ring is, I think, obviously an addition, made to hold the plates rigidly in a circular form when the crown was dedicated to be hung over an altar and no longer needed to be flexible. The gold crown, in fact, was the original thing and the iron ring was a purely subordinate feature added later for practical purposes.
It was only afterwards that the idea occurred to some genius, who observed the iron ring and not the necessity for it, that the gold and jeweled crown was a mere decoration and setting for the iron ring, which therefore he concluded must have been an exceedingly precious relic, ergo one of the crucifixion nails. A little consideration will show that if the iron ring had been the original feature, no one would have made a decoration for it out of hinged plates, for the hinges would have been both a useless and even a troublesome feature. Nothing, in fact, is less like a decorative addition to a ring of iron than these gold and jewelled plates, which obviously were intended for no such purpose. The iron ring exists to support them, not they to decorate it.