The relic and reliquary of St. John the Baptist in Siena (Italy) and their gems.

• New insight on the journey of "Byzantine gems" from the East to the West of the Empire. • The gems of the relic of St. John the Baptist and its reliquary are analyzed for the first time. • The presence of a rare and exquisite example of Balas ruby was identified in the relic. • The investigation improves knowledge on ancient gems traveling across Europe. Gems, especially from remote areas, were highly demanded and valued in Byzantine times, often used for sacred Imperial purposes. Because of their imperishable nature, they were often re-used over time and many of them passed, one way or another, from East to Western Europe. The history of the gems set in Byzantine relics that survived in medieval Europe is often impossible to reconstruct. The exceptional opening of the relics of St. John the Baptist in Siena, 200 years after the last inspection, has made it possible to study the magnificent gems that adorn it. Spinels, rubies, sapphires and other gems from oriental geographies, along with high quality glasses used together regardless of their monetary value, were identified in the relic and its reliquary case through gemological analysis and portable Raman spectroscopy, once again demonstrating the vital contribution of the trans-disciplinary approach in the study of ancient art goldworkings. [ABSTRACT FROM AUTHOR]