The dome was supported on four piers, united by arches, and the change in plan from these piers to the dome necessitated vaultings from the inner angles to reconcile the diagonal dimension to the diameter of the imposed circle. These vaultings spreading from the angles are technically known as Pendentives. The
No. 35. Byzantine. Section and plan of St. Vitali, Ravenna.
No. 36. Byzantine Capitals from Ravenna.
four arms of the cross constituting transepts, nave and chancel were also surmounted by either complete or semi-domes.
The Byzantine dome differs from the Roman type in matters of detail, thus the interior surface is plain instead of the intersecting ribs with resulting coffers as in that of the Pantheon. In this latter the lighting of the interior is accomplished by a central opening or eye, but in some Byzantine examples, notably St. Sophia (built for Justinian by Anthemius) the lighting is the result of windows ranged round the base, constituting what is known as the ariel type of dome.