Basilica of San Vitale - Ravenna (Italy)
The Church of San Vitale, the masterpiece of Byzantine art in Ravenna. Construction began in 526 by Bishop Ecclesius under the Ostrogothic queen Amalasuntha (d. 535) and was consecrated in 547 during the reign of the emperor Justinian. This octagonal church, built of marble and capped by a lofty terra-cotta dome, is one of the most important surviving examples of Byzantine architecture and mosaic work.
virtual tour here