Ravenna had incredible mosaic pictures in its 5th and 6th century churches. The one here shows Abraham's life, where he served lunch to the three angelic messangers, and then later was willing to sacrifice Isaac. Notice God's hand coming out of the sky to stop his sword. This picture doesn't come close to showing the way it really looks. The picture was dark, and the software that lightened it up also made it grainy. I bought a book with professional photos, but even they don't really show you what it's like. Ya just gotta see the mosaics in person.