Symbol of St. Luke (160 x 140 cm.)The highest mosaic register on the wall of the frontal above the apse in S. Apollinare in Classe depicts the symbols of the Four Evangelists who, in a scene of apocalyptic flavour and two by two, flank the bust of the Saviour who, giving his blessing, holds a book, inscribed in a clipeus among the clouds as an image of parousia. The layout of the four symbols is somewhat surprising in comparison with analogous representations: a unique order is not usually followed. Here there is a certain rationality inasmuch as Matthew and John stand in canonical and hierarchical sequence on Christ's right while Mark and Luke are on his left. This is an absolutely orthodox composition since Matthew and John (being Apostles as well as Evangelists) must stand on the right while Mark and Luke, Evangelists only, must stand on the left. Furthermore, as Mark was a disciple of Peter (who has primacy over Paul whose disciple Luke was) it is Mark himself who deserves first place on the left. So Paul's disciple Luke is on the extreme left. This is humanity's evaluation in an interpretative ecclesiastical tradition established after the end of the 4th century.