With around a dozen new high-rises under or shortly to start construction, the Paris business district of La Défense is currently experiencing its third spring. The development of the district started with a building which is arched over by the largest reinforced concrete shell structure built to date. The roof of the Centre des nouvelles industries et technologies (CNIT), which was built in 1958 as an exhibition hall for the French association of machine tool manufacturers, measures 218 m in span and 46 m in height.