Analysis of information sources in references of the Wikipedia article "Late antiquity" in English language version.
[...] engraved gems, found in late antique assemblages or set into late antique jewellery, often represent objects from an earlier period of time. [...] The material worth of older items made them popular in times of uncertainty, especially on the frontiers and border regions of the empire. Furthermore, the skills required to engrave gems declined during the late antique period, meaning that older gems were used in jewellery instead of new carvings being made.