Basilica San Vitale, Christ Enthroned

The Basilica apse of St. Vitale in Ravenna Italy was created in 527 when under the rule of the Ostrogoths by the Bishop, and was completed by the 27th Bishop of Ravenna in 548, during the Byzantine Exarchate of Ravenna.  Until the conversion of Constantine in 312 C.E. Christians worshiped privatly in their homes.  When the emporer legalized christianity and ultimatly converted, christianity became a public faith and there was a new demand for christian art.  The piece on the right is called Christ Enthroned.  It is the mosaic of Apse in the church of San Vitale.  Christ in the apse is represented seated on a globe from which flow the four rivers of paradise. Christ holds in his hands a sealed book which is probably the Book of Life, which Christ will have at the time of the Second Coming and Last Judgment. http://www.sacred-destinations.com/italy/ravenna-san-vitale

The second comparable piece on the left is found in the Basilica Dei Santi Cosma e Damiano in Roma, Italy during the 7th century.  Santi Cosma e Damiano was the first church to be founded in the Forum. In 527, Pope Felix IV (526-30) converted a rectangular apsed hall in the Forum of Peace into a church by the simple addition of an apse mosaic (which survives) and some church furnishings.  The mosaic you see here, is called the Majestas Domini or "Christ in Majesty". 
The 6th century apse mosaic in the Byzantine style is original and justly famous. It is illuminated by a coin-operated light in the left aisle. It provided inspiration for many later mosaics. It depicts the Parousia or Second Coming of Christ "on the clouds of Heaven with power and great glory" (Matthew 24:30). The manner in which Christ is depicted is Roman rather than Byzantine, despite the obvious Byzantine style of the work as a whole.
The mosaic features Christ standing on red clouds (representing the dawn), dressed in golden robes labeled with the monogram I. He holds the scroll of the Law in his left hand. Saint Peter presenting Saint Cosmas, and Saint Theodorus (right), and Saint Paul presenting Saint Damian and Pope Felix IV; the latter holds a model of the church. http://www.sacred-destinations.com/italy/rome-santi-cosma-e-damiano

Notice that both are within domes of space and are "risen" like they are of high importance.  They both capture christ in the middle with little destraction sourrounding.  In my oppinion they feel calming and reassurant of the faith and what may be to come.  Majestas Domini presents the lambs under their feet and abundant sky.  Christ Enthroned suggest nature and simplicity to me. Both of these amazing mosaics use extraordinary color and send a powerful message.