Jewelled Byzantine and Medieval Reliquaries of the True Cross: Peridots and Other Gemstones in Material and Symbolic Perspective

Jewelled crosses containing relics of the True Cross occupy a central position in the devotional, artistic and symbolic traditions of Christianity. Beyond their liturgical function, the selection and arrangement of gemstones has layered meanings associated with protection, sanctity and divine renewal. This study examines three exceptional examples of jewelled crosses—the Crux Vaticana (6th century; Treasury Museum of St Peter's Basilica, Vatican City), the Enkolpion of Constantine (10th–11th century, Treasury Museum of St Peter's Basilica, Vatican City) and the Holy Cross of Castiglion Fiorentino (13th century; Municipal Art Gallery, Castiglion Fiorentino, Arezzo, Italy)—with particular emphasis on the coloured gems adoring the reliquaries and the archaeogemological questions they raise. A noninvasive, in situ analytical approach was employed, based on gemological observations and portable Raman spectroscopy, supported by portable x-ray fluorescence (XRF). Among the identified gems, the characteristic Raman doublet at approximately 822 and 855 cm−1, allowed secure identification of several green stones as peridots [(Mg,Fe)2SiO4], constituting the first analytical confirmation of peridots on these three important reliquaries and enable a coherent gemological mapping of their decorative schemes. In addition, comparative gemological observations suggest a probable provenance from the island of Zabargad (St John's Island, Red Sea), the principal historical source of high-quality peridot in antiquity. In addition to peridots, further gemological and Raman analyses enabled the characterization of several other gemstones. The combined spectroscopic and gemological evidence indicates that while a number of stones are original, others represent later substitutions, attesting a complex histories of maintenance, repair and restoration. The presence of non crystalline materials such as coloured glass further reflects changing material choices over time. Beyond mineralogical identification, this study contributes to the broader debate on materiality and symbolic meaning in devotional ancient jewellery. By integrating Raman spectroscopic analysis with art-historical perspectives, it demonstrates how gemstone choice—particularly the preference for green stones—played an active role in shaping the spiritual and symbolic meaning of True Cross reliquaries.