2.7 – The 19th century set the stage for the explosion of Diagonality in the 20th century. Cast-iron structural frames with diagonal bracing were used to erect vast exhibition halls. Triangulated steel colliery towers rose out of the landscape, foreshadowing and possibly inspiring the angled commemorative towers and speakers’ platforms of the Russian Avant-garde. Iron and steel were also used to create diagonally-braced bridge trusses and suspension structures such as the Brooklyn Bridge. When Lewis Mumford, a 20th century social and architectural historian, first saw the suspension cables slanting off the massive Gothic-styled stone towers of the then-new Brooklyn Bridge, he sensed ‘the dawning of a new age.’ In other design disciplines, particularly the fine arts, there was a move toward geometric abstraction and a concurrent move away from the traditional forms of expression of the previous centuries.