text: Several buildings used by the clerics of the chapel were arranged in the shape of a latin cross: a curia in the East, offices in the North and South, and a projecting part (Westbau) and an atrium with exedrae in the West. But the center piece was the chapel, covered with a 16,54 meters wide and 31 meters high octagonal cupola. Eight massive pillars receive the thrust of large arcades. The nave on the first floor, located under the cupola, is surrounded by an aisle; here stood the Palace servants.
  The two additional floors (tribunes) open on the central space through semicircular arches supported by columns. The inner side takes the shape of an octagon whereas the outer side develops into a sixteen-sided polygon. The chapel had two choirs located in the East and West. The king sat on a throne made of white marble plates, in the West of the second floor, surrounded by his closer courtiers. Thus he had a view on the three altars: that of the Savior right in front of him, that of the Virgin Mary on the first floor and that of Saint Peter in the far end of the Western choir.
  Charlemagne wanted his chapel to be magnificently decorated, so he had massive bronze doors made in a foundry near Aachen. The walls were covered with marble and polychrome stone. The columns, still visible today, were taken from buildings in Ravenna and Rome, with the Pope's permission.
  The walls and cupola were covered with mosaic, enhanced by both artificial lights and exterior light coming in through the windows. Eginhard provides a description of the inside in his Life of Charlemagne (c. 825–826):