In the apse of the Greek-columned interior is a delightful mosaic of St. Apollinaris, Ravenna's first martyr and bishop, surrounded by 12 sheep representing the Apostles, with Moses and Elijah in the clouds above him.
The mosaic uses tiles of only four colors to achieve a surreal, dreamlike quality. 
mnli hypothesis: The mosaic uses tiles of only four colors to achieve a surreal, dreamlike quality.  premise: In the apse of the Greek-columned interior is a delightful mosaic of St. Apollinaris, Ravenna's first martyr and bishop, surrounded by 12 sheep representing the Apostles, with Moses and Elijah in the clouds above him.