Charlemagne (Karl der Grosse in German), the first Holy Roman Emperor, began building his Palatine Chapel (palace chapel) in 786 AD. The Palatine Chapel has been described as a "masterpiece of Carolingian architecture" and was made a UNESCO World Heritage Site in 1978. It is all that remains today of Charlemagne's extensive palace complex in Aachen.
The Palatine Chapel was designed by Odo of Metz. He based it on the Byzantine church of San Vitale (completed 547 AD) in Ravenna, Italy. This accounts for the very eastern feel to the chapel, with its octagonal shape, striped arches, marble floor, golden mosaics, and ambulatory. It was consecrated in 805 to serve as the imperial church.