Mass structures are solid and heavy, providing stability. Examples include mountains, walls, and dams. Truss structures are composed of triangles forming bars, making them lightweight and sturdy, seen in cranes and bridges. Suspended structures are held aloft by cables attached to supports, as seen in bridges, tents, and stadiums. Vaulted structures use arches and stones to form roofs, as in cathedrals, mosques, and some bridges.