was also the first time that a cantilever support system was used to aid bridge construction, with the arches being built outward from the piers, secured by guy wires, and used as platforms from which to continue construction until the two halves of the arch met.19 This method reduced the need for expensive scaffolding but, more important, was – to all practical intents and purposes – the only way to build a large bridge across the wide, deep and fast-flowing Mississippi.
The opening of the bridge on 4 July 1874 was a gala event. The poet Walt Whitman was present and soon declared the bridge ‘perfection and beauty unsurpassable’. A few days later, having had the aesthetics of his bridge so pleasingly praised, Eads demonstrated the solidity of the bridge to a wondering public by leading an elephant over its spans and then, realising this was perhaps not quite convincing enough, sent fourteen locomotives across the bridge, one after the other. The bridge (now known as Eads Bridge) was indeed a modern wonder. Popularly regarded as beautiful, evidently strong, and a record-breaker because its length of 1,964 metres made it the longest arch bridge in the world. Eads’ bridge was in many significant ways a model for, and portent of, things to come.
The Eads Railway Bridge across the Mississippi at St Louis. Started in 1867 to the designs of James Eads, the bridge pioneered the large-scale use of steel in construction and when completed in 1874 was the longest arch bridge in the world.
CHAPTER ONE
EMPIRE
The Pont du Gard, near Nimes, France: an aqueduct built around 2,000 years ago and one of the greatest surviving monuments from the Roman world. The stone blocks projecting from the pier serves as supports for timber scaffolding and centering during construction and maintenance.
ROME, MORE THAN ANY EARTHLY POWER BEFORE or since, expressed its might and its aspirations through architecture and engineering. It took the architecture of the past – of the Egyptians, the Greeks and the Etruscans – and transformed it to suit its own needs and to realize the demands of its growing empire. New functions such as roadways and water supplies emerged, demanding new types of buildings, and these could only be achieved through a radically evolved understanding of the potential of engineering. A series of spectacular developments took place, notably the rapid refinement of structural systems incorporating round-headed arches and domes, giving rise to buildings of unprecedented scale and complexity in which new materials such as concrete (see page 312) were used in major roles for the first time. Roman bridges are a perfect illustration of how awe-inspiring beauty can emerge from innovative engineering.
Rome’s breathtaking and groundbreaking contribution to the development of architecture was characterized by an ever-growing appreciation of the potential of engineered structures in which the forces of nature were harnessed and tamed to complete projects that would have been beyond even the imagination, let alone the practical grasp, of earlier generations. The resulting structures combined the cardinal architectural virtues identified by the Roman architect Vitruvius over 2,000 years ago – ‘commodity, firmness and delight’ – by which he meant an architecture that simultaneously fulfils its functional requirements and is stable, while also being poetic and imbued with a power to inflame and engage the intellect.
The aqueduct in Segovia, Spain, constructed during the 1st century AD, snakes through the town, its conduit supported on increasingly tall tiers of arches as the ground level falls away.
Roman architecture, at its best combining sublime beauty with function, often played a vital role in consolidating and spreading Roman power and maintaining its civilization. This fascinating combination of characteristics is perhaps best expressed by the bridges and aqueducts that Rome created throughout its empire. Their roles as routes of communication and the means of supply were of vital importance to the well-being of the Roman world. Aqueducts brought a plentiful supply of water – essential for the Roman concept of civilized life – and roads transported goods and luxuries over great distances, allowed wealth creation through trade, and security through speedy troop movements. In addition to being functional objects, bridges and aqueducts were also intended, in their design and solidity, to express Rome’s cultural aspirations and the longevity of its vision. Together, these intentions produced structures of intense beauty – a beauty that comes from the pure and powerful realization of functional demands and of the way in which the potential of available building material can be enhanced through design.
A remarkably large number of Roman bridges survive, in whole or in part, still fulfilling their original function within the former empire. They continue to astonish, inspire and delight, through their scale, fitness for purpose and often daunting engineering boldness. But there are four Roman bridges that haunt my imagination. They epitomize Roman engineering genius, in which sublime and utterly moving beauty is achieved by the almost ruthless observance of function. They are the essence of engineering, and also the essence of architecture at its best. There is little about their design and construction that is superfluous to function or to pertinent meaning. Their stones carry messages, about the power of engineered structure and about the seemingly eternal power of Rome. In all these bridges each detail possesses an intensity of meaning and beauty: even those that appear ornamental are in fact calculated to add extra cultural or spiritual significance, raising purely utilitarian design into the poetic realm of architecture.
All of these structures lie outside of Italy. Two of them, the Pont du Gard in southern France near Nîmes and the aqueduct of Segovia in Spain, carried the very life-blood of Roman civilization: abundant water. The others, the Alcántara Bridge over the River Tagus in Spain, and the Pont Flavien, in Saint-Chamas, Bouches-du-Rhône, France, seem to have served a largely military, strategic and triumphal purpose marking the omnipotent presence and power of Rome. But each one, in its solidity and scale, seems to have been built in defiance of nature. And yet this is not quite so, for it is the essential paradox of engineering that the violence of the forces of nature can only be withstood by man-made structures that fully utilize the forces of nature. The fact that these structures survive after 2,000 years or so – with all significant damage being the work of man and not natural forces – demonstrates most succinctly how well these Roman engineers understood their work.
The Pont du Gard is a stupendous aqueduct located about 29 kilometres north of Nîmes. As its name suggests, it spans a valley through which the river Gard winds. It forms part of a conduit constructed to carry the waters of the Alzon some 50 kilometres to Nîmes and, rather appealingly, no one is absolutely sure of its date. The current consensus of opinion is that the aqueduct was started by Marcus Vipsanius Agrippa, the brother-in-law of Emperor Augustus in about 18 BC and that the Pont du Gard itself is around 2,000 years old, although some argue that it dates from the mid first century AD. But what is more certain is that the Pont du Gard is one of the most moving and awe-inspiring structures to survive from the ancient world. The first glimpse you get of it is a virtual assault on the senses: its scale is majestic, its form intensely pleasing and it soon becomes clear that most of the architectural details that it sports are not merely ornamental but are expressions of the means of construction.
An intimate view of Roman precision engineering: a vista along the conduit on top of the Pont du Gard. This is the only place in the structure where mortar was used – necessary to ensure water did not leak through the joints in the masonry.
The aqueduct has an overall length of about 262 metres and comprises three distinct tiers of structure. The lower tier is formed by six wide arches (each spanning a distance of something between 15.2 and 24.3 metres) which support a roadway. From this roadway rise arches similar in size to, and with their piers set over, those below. But this second tier is made up of 11 arches because the cliff faces forming the river valley taper dramatically as they rise higher. On top of the second tier sits