Early mosaics before this time period had been used as a cheap floor covering. Very quickly it was discovered that the mosaic medium lent itself to simple geometric patterns that were simple and decorative. These mosaic floors were usually just small stones of varying sizes. The next step in mosaic work was to incorporate pictures and more complicated designs (Kleiner and Mamiya 315).
As time passed new methods were introduced to mosaics that allowed the artists to create more detailed mosaics with shadowing and cleaner outlines. One of the methods was to use tesserae, or tiny stones cut into cube shapes that could be adjusted for different sizes and shapes easily. Greater color gradations were introduced as well, giving mosaics an almost painted look. During the Early Christian Era the tesserae were generally constructed out of glass to give the mosaic a glittering look. The Romans, however, tended to use marble tesserae (Kleiner and Mamiya 313).
The mosaics in Christian churches were not meant to show subtle contrast and smooth changes like a typical painting, but were meant to be bold and powerful pieces of art designed to inspire. These mosaics decorated wall upon wall of Christian churches and used larger stones instead of the smaller Roman ones,
Bibliography: Demus, Otto. The Mosaic Decoration of San Marco Venice. Washington D. C. : The University of Chicago Press, 1988. Kleiner, Fred S., and Christin J. Mamiya. Gardner 's Art Through the Ages Volume I. Twelfth Edition. Belmont, CA: Wadsworth, 2005.