It is difficult to define Ciborium for while it generally means a fixed rectangular structure above the altar, usually open on all sides, its use has been enlarged to indicate other parts such as the tabernacle. This arc has intertwined decorations with two facing peacocks. The peacock became a widely used symbol for early Christians thanks to the legend of the classical period which considered peacocks’ meat to be incorruptible. From this the Christian symbol and identification with Christ and the Resurrection.
It is possible that the object was part of the high medieval church of dedicated to the patron saint which existed in the 7th century on the hill of San Lorenzo (the present day Duomo hill). It was later substituted by the building of the present day Cathedral.