It was the Romans who first fully realized the architectural potentialities of the dome. The Roman development in dome construction culminated in the pantheon (2d cent. A.D.). The Romans, however, failed to discover a proper handling of the pendentive—the device essential to placing a dome over a square compartment—that was finally achieved by the Byzantine builders of Hagia Sophia at Constantinople (A.D. 532–37). The other solution to placing a dome over a square was the squinch, which in the form of stalactites was to receive superb expression in Islamic architecture. Under Byzantine influence the Muslims early adopted the use of the dome; one of their first important monuments is the Dome of the Rock in Jerusalem. They often used the so-called Persian or onion dome. The most celebrated example is the Taj Mahal (A.D. 1630) at Agra, India.