The Church of Saint Peter in Chains contains, as the name suggests, the chains that held Peter when he was imprisoned in Rome. They are prominently displayed under the altar. The story about the chains can be a bit confusing. At its core, the chain that held St. Peter was divided at some point in its history, with half going to Jerusalem. It was returned to Rome, however, and upon being placed with the other half, to two pieces joined to become one.