Today’s feast day (prior to 1960, anyway) commemorates the consecration of the Basilica of St. Peter ad Vincula (“at the Chains”). That’s the basilica in Rome that houses a major relic of St. Peter. It’s a single chain formed from two separate chains, one that bound St. Peter when he was imprisoned in Jerusalem and one that bound him when he was imprisoned in Rome. When the two chains were brought together in the 400s, they miraculously fused together.*
Here are some photos that I took at the basilica in 2007. First, the miraculous chain. The reliquary is located in the confessio (crypt shrine) below the basilica’s high altar.
Next, Michelangelo’s famous statue of Moses from the tomb of Pope Julius II, which is located in the basilica:
Finally, a closer view of Moses:
*See the New Liturgical Movement article for the backstory on the feast, church, and relic: http://www.newliturgicalmovement.org/2017/08/liturgical-notes-on-feast-of-st-peters.html#.WYD-JWdK2M8