In architecture, a hemispherical structure evolved from the arch, forming a ceiling or roof. Domes first appeared on round huts and tombs in the ancient Middle East, India, and the Mediterranean in forms, such as solid mounds, adaptable only to the smallest buildings. The Romans introduced the large-scale masonry hemisphere. A dome exerts thrust all around its perimeter, and the earliest monumental examples (seePantheon) required heavy supporting walls. Byzantine architects invented a technique for raising domes on piers, making the transition from a cubic base to the hemisphere by four pendentives. Bulbous or pointed domes were widely used in Islamic architecture. The design spread to Russia, where it gained great popularity in the form of the onion dome, a pointed, domelike roof structure. The modern geodesic dome, developed by R. Buckminster Fuller, is fabricated of lightweight triangular framing that distributes stresses within the structure itself.