Almost on every visit I take a picture of the dome (on some visits it was covered by scaffolding due to restoration), which has its highest point at 56 meters. It is slightly elliptical, with 31 meters along the east-west diameter, 33 along the north-south diameter. It has fourty ribs that radiate out from the crown, separated at the base by 40 windows of which 4 were blocked during repairs in the tenth century.