Pendentives are spherical triangles. They transmit the weight of the spherical dome to round arcs. These arcs support the dome in such a way that the weight of the dome is concentrated unto the colums at the angles of the square base of the dome.

The domes of the San Marco basilica (from 1060 until 14th century) are probably the most beautiful example of the use of pendentives. Five domes, finished with mosaics are placed adjacently. Pendentives make the transition from square tot circle.

The plan of the basilica has the form of a Greek cross (= a cross with 4 equal arms) with one central dome and four domes placed on top of the arms of the cross.