reliquary and royal insignia
via Wikipedia infobox
The Iron Crown (in Italian, Latin, and Lombard: Corona Ferrea; German: Eiserne Krone) is a reliquary votive crown, traditionally considered one of the oldest royal insignia of Christendom. It was made in the Middle Ages, consisting of a circlet of gold and jewels fitted around a central silver band, which tradition held to be made of iron beaten out of a nail of the True Cross. In the later Middle Ages, the crown was used as regalia for the coronation of some Holy Roman Emperors as kings of Italy. It is kept in the Duomo of Monza.
Description
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).