Spolia is the Latin term for "spoils" and is used to refer to the taking or appropriation of ancient monumental or other art works for new uses or locations. We know that many marbles and columns were brought from Rome northward during this period.
Perhaps the most famous example of Carolingian spolia is the tale of an equestrian statue. In Rome, Charlemagne had seen the Equestrian Statue of Marcus Aurelius in the Lateran Palace. It was the only surviving statue of a pre-Christian Roman Emperor because it was mistakenly thought, at the time, to be that of Constantine and thus held great accord—Charlemagne thus brought an equestrian statue from Ravenna, then believed to be that of Theodoric the Great, to Aachen, to match the statue of "Constantine" in Rome.
Antique carved gems were reused in various settings, without much regard to their original iconography.
Read more about this topic: Carolingian Art