Jeremy Melvin

Its deck poised like a tensed bow over the water and tantalisingly tied to a parabolic arch tilting just backwards from vertical, Gateshead's Millennium Bridge has joined the veritable gallery of imaginative structures with which numerous engineers have spanned the River Tyne over the last 200 years. Stephenson's high-level railway girder bridge, Armstrong's delicate swing bridge that seems to skim across the water, and Mott Hay Anderson's dry run for Sydney Harbour all used the most advanced technology of their time to produce iconic structures, showing that innovation in engineering can also be aesthetically beautiful. The Millennium Bridge is assured and certainly iconic. Its opening mechanism of vast trunnion bearings and hydraulics concealed in either bank is definitely innovative, yet it also seems to embed traces of the arch of the Tyne Bridge, the opening of the Swing Bridge, and the vantage point of the high level bridge. And when it opens, in a movement as graceful as an accelerated film of an unfolding flower, it appears to bow to its venerable neighbours.

Such a multi-faceted aesthetic experience adds to the safety that modern engineers can provide as a matter of course. It is the essence of the architectural sensibility that WilkinsonEyre brings to bridge design. The practice's analysis and designs refer to the history and character of their locality, and enrich the experience of those who use the bridges, by offering new views of the area, or inviting them to linger and look. Making bridges beautiful as well as useful is something designers would have taken for granted up until the middle of the 20th century but, as engineering split from architecture, it increasingly pursued economy and efficiency above all else. The importance of aesthetics became downgraded and the results impoverished our environment as the splendour and awe that bridges could inspire, and their potential as landmarks, was passed over.

The plaudits attracted by the Millennium Bridge from the Stirling Prize jury as well as locals and visitors to Newcastle or Gateshead may have redressed the balance, but it is far from the only WilkinsonEyre bridge to inspire awe in its observers. The tiny footbridge at high level across the atrium in the Science Museum's Challenge of Materials Gallery probably has more innovation than many a motorway viaduct. The bridges on the Channel Tunnel Rail Link and the design for the East Span across San Francisco Bay showed what the control of space, light, form and material can bring to the largest structures.

Or imagine driving along a highway through the mountainous wilds of northern Greece. On either side the landscape has changed little since classical times. Maybe the shepherds and their sheep who dapple the unforgiving mountainsides are descendants of those who heard how the Athenians defeated Xerxes' vastly superior Persian army at Thermopylae. Entering a tunnel brings back the modern world, but coming out again into the harsh sunlight, the mountain falls away and the road continues as if onto a ray of hovering asphalt. 'Wonders are many, and none more wonderful than man, who rides the ocean and takes his way through the deeps, through windswept valleys…' The refrain Sophocles wrote for the chorus in his great tragedy Antigone might seem to resound even in a totally different, contemporary context – or, indeed, for any of WilkinsonEyre's bridges.

Rock-anchored into the mountain behind the tunnel mouths, the suspension cables seem held from the sky; almost invisible, the catenaries are like the gossamer threads by which Mount Olympus' capricious inhabitants toyed with the lives of mortals. Were it to be built, the Metsovitikos Bridge on the highway across northern Greece, a project intended to bring modern development to a developing part of Europe, captures the spectrum of time, place, function and culture in a compelling design aesthetic.

Above all WilkinsonEyre's bridges evoke associations which encompass the banal or sophisticated, the personal or collective, that make up our culture. In their hands bridges are scientific and artistic, innovative and associative, in a way that is alien to many modern engineers. Few architects share the intuitive understanding of structural principles that allows the practice to form such fruitful working relationships with engineers. This synthesis is what architecture offers contemporary bridge design. Architects can develop a thread that links such specialist knowledge to the realm of social use and meaning.

Jim Eyre likes to illustrate this with Christian Menn's diagram of three concentric rings around a circle depicting the sequence of aims that bridge designers follow. The outermost is safety, then follow serviceability and efficiency, with aesthetics in the centre of the target. Hitting the bull's eye is essential if a bridge is to be more than a simple means of getting over an obstacle – if it is to achieve its potential as a landmark or to recognise the social importance it might have as an agent of urban regeneration. Eyre always aims for the bull's eye, where aesthetics add a delicate dance of value around the prosaic function, but success depends on being able to follow through the entire project, from concept to detail. Gateshead, for example, looks in reality remarkably like an initial sketch, an effect that comes from extraordinary consistency of thought and detail.

WilkinsonEyre's first bridge, designed in 1994, was the sinuous South Quay Footbridge spanning 180m between Heron Quay and South Quay. It was one of several innovative designs built by the LDDC shortly before it was wound up. Around the same time flamboyant bridges were winning opprobrium from engineers, precisely because they do not follow the most economic structure, but their acclaim from architects and evident popularity with the public suggested that something was missing from the pure engineering approach. Having established an architectural philosophy encompassing such necessary attributes in bridge design as lightness, innovation in materials and long spans, the practice was in a strong position to capitalise on these new opportunities. With its deft touch – a pair of canted masts suspending the dual curves of the deck – the South Quay bridge took interests in lightness and long spans – that Chris Wilkinson's book Supersheds and the Stratford Market Depot had made explicit as early as 1991 – into the realm of bridge design. It also began to explore a fascination with movement, a quality Chris Wilkinson brackets with space, light, form, structure and material, as the essential constituents of architecture. Originally built in two parts so it could be relocated in shortened form as land was reclaimed one part can swing open to allow boats through.

In designs for displays at the Science Museum, Explore@Bristol and Magna, WilkinsonEyre has explored the potential of buildings to be interactive and convey information. The idea of opening bridges at South Quay and Gateshead brings that potential, embryonically, to bridge design.

In each project WilkinsonEyre brings its established interests into a different relationship. A shed, with a vast roof floating may demand lightness and a long span, but it creates a zone of universal space, rather than a single, specified route as a bridge does. Jim Eyre writes that there are only three basic types of bridge structure: a truss or beam, an arch, or a suspension or cable stay structure. But within that choice the range can be endless. An arch might be circular or parabolic; a beam might be a simple supporting structure or a box girder, while there is a huge aesthetic difference between the dipping catenaries of a suspension bridge and the varied angles of each rod in a cable stay structure. Another layer of variety comes from the choice of material, and driving this matrix of selections is a realisation that the clear physical condition of linearity that bridges have can begin, through narrative to symbolise other less tangible ideas.

There is a school of thought suggesting that the best-engineered bridges are finely balanced compositions, working with absolute efficiency whose merit is not reliant on the context of their surroundings. The poet Philip Larkin captured this view when he described the 2220m long Humber Bridge as 'swallow fall and one plane line'. There may not be the same scope for expression in the 32m of Bedford's Butterfly Bridge, or the twisted frames of the Royal Ballet School's bridge across Floral Street, but there is some.

Perhaps the most graphic illustration of the way WilkinsonEyre makes a bridge convey ideas, as well as carry a route from A to B is the footbridge in the Science Museum's Challenge of Materials Gallery. Function and meaning coalesce in a structure that consciously pushes its materials, primarily steel and glass, to the utmost. The taut cable stays, which can be played like a musical instrument, describe graphically the extreme roles that all its components play. All parts are equally essential, as if the flows of Naum Gabo's Linear Construction are frozen into the stasis of Ken Unsworth's Suspended Stone Circle II, and then transformed into a structure which is not only useful, but also has a didactic purpose. The extraordinary sensation of the Metsovitikos Bridge design, or the frisson of seeing the Gateshead Bridge open, as if upturned by the wind, are focused into an appreciation of the human ingenuity behind materials, and the calculations and designs that organise them. As Sophocles said, 'Wonders are many, and none more wonderful than man'.

This piece appears in the book 'Bridges' (WilkinsonEyre 2003).