In the 1950s and 60s, spanning great distances was central to many architectural visions. Today, although pragmatic, economic considerations are likely to prevail, large-span structures still exercise a fascination for architects and engineers. In recent years, a great number of halls have been realized, the roofs of which are remarkable for their broad spans. At 240 m, the Georgia Dome in Atlanta (ill. 9) has the largest span in the world. The Seibu Dome, erected in 1999 in Tokorozawa, Japan, has a clear span of 220 m; and the Sapporo Dome, at present under construction, will enclose a football stadium and span a distance of 218 m.