The development of tesserae, a manufactured tile that was capable of great variation in color, size and shape that made great detail as well as subtle color changes possible. Sometimes these tesserae were very tiny pieces, allowing the artist to paint with tile.
In the 5th century, the city of Ravenna became known as the city of mosaics. The best known building in the city is the mausoleum of Theodoric, a king of Byzantium. The best known mosaic is the mosaic in the cathedral built for this same king, but now renamed Sant’Apollinaire Nuovo. The scenes in this cathedral featured images of Christ as well as images of Theodoric and his household. Many of those have been replaced by later rulers; interestingly, there is a scene of the Emperor Justinian and the Empress Theodora. This is interesting because the images of Theodoric were removed because the principle of having no images of a ruler in a cathedral.