An apse lined with mosaics and open to the air still preserves the memory of one of the most famous halls of the ancient palace, the "Triclinium" of Pope Leo III, which was the state banqueting hall. The existing structure is not ancient, but some portions of the original mosaics may have been preserved in the tripartite mosaic of its niche. In the center Christ gives to the Apostles their mission; on the left He gives the Keys of the Kingdom of Heaven to Pope Saint Sylvester I and the Labarum to Emperor Constantine I; and on the right Saint Peter gives the Papal stole to Pope Leo III and the standard to Charlemagne.