At the narrowest point of the gorge, this easy harmony between man and nature is transfigured by one titanic act of engineering into a thrilling, breathless tension. On the city side, a high diagonally-stratified bluff breaks free from the escarpment; upon it stands a colossal tower of rough blue-grey Pennant stone, ninety feet high and thirty broad, the huge apertures scooped from its craggy flanks opening like portals into the beyond. Two hundred yards away on the Somerset side is a second tower, perched on an artificial outcrop of blood-red sandstone. Between them run the great chains: anchored in bedrock two hundred feet back on each side, they rise to pass through square openings beneath the parapet of each tower before looping down and up across the ravine like iron lianas in a vast hanging curve of tremendous, perilous beauty. Suspended from them on a hundred and fifty slender harpstring rods is the roadway, a shallow deck of planks and girders overlaid with tarmac; it is so narrow that traffic must go in single file, the cars seeming to pick their way nervously across like tightrope walkers uncertain of their safety net.
The mastermind of all this high-wire artistry was, of course, Isambard Kingdom Brunel; and this, perhaps his best-known surviving structure, is the famous Clifton Suspension Bridge. The bridge was both Brunel's debut and his epitaph. When he won the competition in 1830 he was a young man of 24, the son of a leading engineer but with no major independent projects to his name. He had submitted several alternative schemes, of which his favoured option was for a much longer bridge without towers, hanging below the level of the hill-tops and accessed via a pair of access tunnels cut through the cliffs. This proposal, with a span of nearly 1000 feet, was dismissed as a physical impossibility - although the design that was eventually accepted still required a 700-foot span, far longer than any then in existence.
Brunel never saw his bridge completed, or even properly begun. By the time he died in 1859, work had been abandoned for more than a decade due to lack of funds, with only the two half-finished towers eyeing one another up like stone vultures from either side of the unspanned gorge. The chains and deck were finally installed as a memorial to Brunel in 1864, under the joint supervision of John Hawkshaw and William Henry Barlow. Economies were still required: the chains, for instance, are second-hand, having been brought from Brunel's lately-demolished Hungerford Bridge across the Thames at Charing Cross.
Clifton was by no means the first suspension bridge (rope-bridges of this type go back to antiquity, and a version using iron chains was pioneered in North America at the beginning of the 1800s), and by the time of its belated completion it had long since been surpassed in terms of length and load-bearing capacity. What Brunel did was to give the form its first definitive artistic expression. Recent discoveries in Egypt offered the early 19th century a new idiom in which to express the sense of awesome power and majesty that the engineering marvels of the day inspired. The form of the towers, with their battered (that is, inward-sloping) walls and cavetto (quadrant-shaped) cornices, deliberately recalls the massive pylon gateways at such temples as Philae, Luxor and Edfu, and was calculated to draw forth from the myth-kitty the same images of hieratic power and enduringness that Shelley had recently employed, albeit to more ironic ends, in 'Ozymandias'.
But it is less the style, which soon fell from fashion, than the sculptural quality of the towers that has proved so iconic: their hunched, Atlas-like aspect, as if they stood with legs apart and knees bent to bear the weight of the unimaginable; the elemental simplicity of their outlines, and of the great geometric openings - rectangular, segmental, parabaloid - cut clean through their solid masonry, suggesting both oneness with and transcendence of the fissured limestone landscape they bestride. In fact, the rough-hewn sublimity that is the structure's defining characteristic results as much from what Hawkshaw and Barlow left out as what Brunel put in. The latter had envisaged a full programme of neo-Eygptian embellishments, including paired sphinxes atop the towers and sheet-metal cladding emblazoned with sun-disks and faux hieroglyphics, all of which would soon have made the bridge into a mere charming period piece. In its final, unfinished form it is a timeless thing: a speaking emblem of the dynamics of human potency, of the visionary intellect imperiously commanding, yet visibly reliant upon, raw collective strength.
The very conception of what, in aesthetic terms, a bridge involves has changed utterly since Brunel's day. Despite its technical brilliance, his great work belongs in many ways to an immemorial tradition of bridge-building that relies for its visual effect on mass and masonry and manifest, overwhelming power. The Brooklyn Bridge in New York, an obvious descendant of Clifton completed in 1883, was among the last to be built according to this Cyclopean paradigm. Through the 20th century, advances in steel and reinforced concrete construction refined the suspension bridge down to an airy, effortless minimum, flung across ever more tremendous distances with the insouciant grace of a harpist's arpeggio. Compared with the tiptoe poise of, say, the 1937 Golden Gate Bridge at San Francisco, Clifton appears positively archaic in its display of ancient archetypes and brute musculature. In this, it perfectly typifies the century of its construction. A child of Romanticism as well as an empirical genius, Brunel sought throughout his life to make structural rationality congruent with historical resonance and poetic grandeur: a notoriously difficult marriage, but here at least a triumphantly successful one.
