A cross of this sort, also known as an ‘enkolpion’, could be worn as a pectoral cross, and was an attribute of bishops during the Middle Ages. Over the course of the centuries, many of these crosses were produced in such a way as to hold a secondary relic. They might contain, for example, relics which were alleged to be part of a saint’s clothing, pieces of the True Cross, or hair fragments. The cross was the most popular Christian symbol in Byzantium: it offered protection to the wearer and would have been available all over the Empire.
IC XC is a monogram for ᾽Ιησου̑ς Ξριστὸς, Jesus Christ. Often the word NIKA is also added and completes the phrase; Jesus Christ conquers.