The Classic Roman Type Mosaic
Mosaics were used extensively in the ancient Roman world and Byzantium was first a classic Roman city. It was more than a century after Constantine established it as capital in the east before the real effects of the empire's adoption of Christianity would show. The Great Place Mosaic Museum has in place a large mosaic that was found where the original imperial place was located. Probably done in the 4th Century or so, it is classic Roman through and through.
These mosaics decorated a large floor area
While the scenes may seem violent they are almost all symbols for certain stories or values.
Let's look at some detail. Notice how each of the tiles used is a square tile. Also note that the artwork that results is somewhat flat and/or stylized
Early Byzantine Christian Type
300 hundred years later in the early 7th century we have Justinian, now a thoroughly Christian Emperor building the Hagia Sophia. There aren't many mosaics that remain from them but here are a few.
Note the changes. Obviously the subjects, here we have Christ, John the Baptist, and in the lower one the Empress Theodora. Notice how the tiles themselves have become much more colorful allowing the mosaic artist to do more with coloring and shading. But when we look at the figures they're still somewhat two dimensional
Late Byzantine Christian Type
One of the ironies of Byzantine history is that as it lost its power, it underwent an artistic, philosophical, and learning revival. Books have been written about how that revival led directly to the Italian Renaissance. The mosaics below are from the Chora Church which was done in the 14th century. These are scenes from gospels that were not accepted into the Roman Catholic Bible.
To me there is much more a sense of flow and movement in the figures, a roundness of form and face, and a greater capturing of emotion. The use of color is more creative as well. Look at this shot of the detail.
The tiles are no longer just square. They have a variety of shapes and wide variety of colors and shades of colors