Hagia Sophia / dome interior & seraph

Main dome of Hagia Sophia (Holy Wisdom), designed in the Byzantine style by Isidore of Miletus and Anthemius of Tralles for Emperor Justinian I, completed AD537. The dome's weight rests on pendentives — spherical triangles that connect to four massive piers. 

One of the seraphim decorating pendentives of the Hagia Sophia. The face has only recently been uncovered (c.2009) since being painted over in the late 1840s. These particular mosaics were probably applied c.1348 during restoration of a partial collapse due to an earthquake. Istanbul, Turkey. 

(CC BY-NC-SA 2.0 - credit: Images George Rex.)