|The Traditio Legis and
The Traditio Legis is an iconographic type in the earliest Christian art. It has Christ with St. Peter, or with St. Peter and St. Paul, handing to one of them a scroll that represents the law, as at left. There was a similar secular type in which the enthroned Emperor hands over a scroll, expressing his role as lawgiver.
In later centuries the "keys to the kingdom" of Matthew 16:13-20 (cached) became St. Peter's primary attribute, and the Traditio Legis image had him receiving the keys while the scroll went to St. Paul (example).
The kind of narrative image that uses keys to represent the episode in Matthew 16 (example) is sometimes referred to as theTraditio Clavum.
At left, 4th century sarcophagus
11th century tympanum