The world's first cast iron bridge, designed by William Williams, was built over the River Severn at Coalbrookdale, England in 1779. The bridge represented a significant moment in the industrial revolution, but in terms of bridge design itself the new technical possibilities offered by iron, and later steel, would present bridge designers with the question as to what sort of aesthetic steel bridges should have.

Before iron and steel, masonry bridges had evolved a clear aesthetic of arches and massive solid forms which allowed ornament to be added by sculpting into the masonry itself. The new engineering options which came with iron meant that bridges structures would have open filigree forms instead of the massive forms of masonry. To what extent did these new structural forms need to be adorned with ornament or concealed to make them aesthetically acceptable?

Whilst the structural functionality of steel bridges was clearly the domain of engineers, should the engineer be trusted to design steel bridges alone without the input of an architect to control its finished appearance. Since Ironbridge it is interesting to see how different bridges designs have included the input of an architect in collaboration with the engineer.

Many early steel bridges were built for railways. Most railway bridges built in environments way from cities were built as essentially pure engineering forms.  Examples of major steel bridges such as the Garabit Viaduct  (designed by Gustave Eiffel and opened in 1884) and the Forth Rail Bridge (John Fowler and Benjamin Baker and opened in 1890) are pure engineering forms devoid of ornament. Though devoid of the intervention of an architect, these bridges have come to be accepted as beautiful pieces of structure. However it is not always the case that pure engineering forms will automatically have a good aesthetic.

In cities, where bridges would be seen by many more people, some steel bridges would be given ornament to dress or even hide the steel structure. The degree to which ornament was added reflected the degree to which societies in different places embraced the engineering aesthetic. The Pont des Arts (Louis-Alexandre de Cessart and Jaques Dillon engineers, 1802) represents an example where the pure engineering is accepted without ornament.  At the other extreme is the famous Tower Bridge in London (Horace Jones, architect, with John Wolfe Barry, engineer, opened 1894) where the steel structure of the bridge towers is completely hidden by an ornamental masonry cladding. More structurally honest bridge designs with limited superficial ornament can be seen in Paris where the structural forms of the Pont Alexandre III (Jean Resal engineer, 1900) and the Pont d’Austerlitz (Louis Biette, engineer, Camille Formige, architect, 1907).

In contemporary bridge design it is rare for superficial ornament to be used as it is considered not to be “honest”. The quality of the bridge aesthetic (whether arch, suspension, cabled stayed, truss, beam etc) therefore  depends of the overall geometric proportions of the bridge and the sculptural form of the engineering elements themselves.  A bridge design can be dramatically improved if its towers and or deck design has been carefully considered as large sculptural elements. Some engineers (e.g. Santiago Calatrava, Marc Mimram) are confident of their own ability to design without collaborating with an architect, however some recent examples show how the successful collaboration between engineer and architect can yield bridges with striking visual appeal.

The Millennium Footbridge in London (Ove Arup & Partners, Engineers, Foster and Partners, architects, opened) which can be compared to the Pont des Arts in terms of its structural expression.

The Gateshead Millennium Footbridge (Gifford and Partners, engineers, Wilkinson/Eyre, architects) which can be contrasted with Tower Bridge in doing a similar job as an opening river bridge. 

The new Millau Viaduct is a design collaboration between engineering and architect  teams (led respectively by Michel Virlogeux and Norman Foster). Whilst the overall proportions of the viaduct were determined largely by technical considerations including its method of construction, the sculptural forms of the piers, masts and bridge deck were developed in close collaboration between engineer and architect teams. As well as providing an important piece of infrastructure in the French road network, the completed viaduct will be a beautiful piece of architectural and engineering bridge design of which the town of Millau can be proud.