Dan Cruickshank’s Bridges: Heroic Designs that Changed the World

(#litres_trial_promo) Construction work, from cutting and transporting stones to raising them into place, was a very important part of the economy of the Roman state. It was a way of creating work and jobs, keeping people employed and out of trouble, and of getting money to flow through society. For example, Emperor Vespasian (AD 69-79) refused to let builders use water-driven hoists ‘lest the poor should have no work.’

(#litres_trial_promo) So in place of mechanical power, the Romans preferred – almost as a matter of state policy – to achieve lifting largely by muscle power, operating cranes or systems of pulley blocks hung from legs or poles and worked by winch or capstan. Using these devices, heavy stones were lifted by slings, or gripped by pincers or a kind of ‘lewis’, a lifting tool comprising metal bars inserted and wedged into a dovetailed cavity cut in the top of a block of masonry.

Detail of the Pont du Gard showing piers rising from the lower arcade. The projecting stones were supports for timber scaffold during construction.

Metal was also used in construction, usually in the form of wrought-iron cramps or bars set in lead and then placed in cut recesses to bond stones together. As Vitruvius explains when discussing how to avoid the problem of crumbling mortar: ‘…leave a cavity behind the [facing wall]…on the inside build walls two feet thick…and bind them to the fronts by means of iron clamps and lead.’ Work executed in this way, Vitruvius claimed, ‘will be strong enough to last forever.’

(#litres_trial_promo)

Vitruvius also had some specific things to say about aqueducts, reminding his readers of the importance of an adequate and reliable water supply and stating that for aqueducts or ‘conduits’ the masonry should be ‘as solid as possible and the bed of the channel have a gradient of not less than a quarter of an inch for every hundred feet, and let the masonry structure be arched over, so that the sun may not strike the water at all.’

(#litres_trial_promo) Vitruvius also recommended that, when the water carried in the conduit reaches the city it should be held in a ‘reservoir with a distribution tank in three compartments.’ The system was intended to segregate water used for different purposes and to prevent people tapping into the main flow and stealing public water for private use.

(#litres_trial_promo) Vitruvius also recognized that water quality was very important, so recommended that it was best to conduct water through clay pipes rather than lead pipes because ‘water from clay pipes is much more wholesome than that which is conducted through lead pipes, because lead is found to be harmful [and] hurtful to the human system.’

(#litres_trial_promo) The evidence for this was the health of ‘plumbers, since in them the natural colour of the body is replaced by a deep pallor’ caused by lead fumes that ‘burn out and take away all the virtues of the blood from their limbs.’

(#litres_trial_promo) Vitruvius’ recommendations seem to have been used by the Rome official Sextus Julius Frontinus who in about AD 80 wrote a treatise on the Aqueducts of Rome, in which he described the condition of the city’s water supply, actions needed to prevent water leaks and theft, and, in general, promoted Vitruvian theory.

An interpretation of a stone-lifting pulley block.

A view of a Roman period water supply system, including covered aqueducts. Both engravings date from 1521 and are based on descriptions by the first-century BC Roman architect Vitruvius.

‘The sight of the aqueduct entering the town is among the greatest surviving urban scenes from the ancient world. It was dedicated to Hercules – the legendary founder of the city – and still seems the work of divine heroes.’

Extraordinarily enough, a physical example of Vitruvius’ recommendations and theory survives to this day in Spain. The aqueduct in Segovia was built about 100 or so years after the Pont du Gard, perhaps in about AD 50–100 and, unlike the Pont du Gard, continues to fulfil the function for which it was built. Thanks to the skill and robustness of its construction, generations of maintenance, self-effacing reconstruction, and the soundness of Vitruvius’ thinking, the conduit and aqueduct retains its Roman identity and still carries water 15 kilometres from the Fuente Frio River to the old city of Segovia. Much of this length is at or near ground level, but due to the terrain near the city, 800 metres of the conduit is supported on arches springing from piers up to 28.5 metres high.

(#litres_trial_promo) Few things are more moving, in the world of ancient engineering, than to see and hear the water – after nearly 2,000 years – still coursing along its worn but serviceable granite conduit perched high off the gnarled, sun-baked and leaping arches of the aqueduct.

The aqueduct, and the conduit it supports, is an admirable machine for gathering and delivering water to an elevated city, the aqueduct’s height above ground varying to accommodate the terrain and to keep the decline of the conduit as little as possible. When the water arrives in the city it is first collected in a tank known as El Caserón (the Big House) and from there runs along a channel to a tower known as the Casa de Aguas (the water house) where it is allowed to decant and impurities settle. The reasonably pure water then travels nearly 730 metres, at a fall of only one-in-a-hundred, to an outcrop near to which the Roman city was built. Then the aqueduct, rising to its full height of 28.5 metres and comprising two levels of semi-circular headed arches, carries the water into the city, to what is now the Plaza de Díaz Sanz. As with the Pont du Gard, the stone blocks – in this case granite – with which the aqueduct is built are unmortared, their precise construction and weight being enough to keep all standing. Particularly satisfying is the masonry of the voussoirs forming the arches, which are a single block deep. They combine with the horizontal courses of the spandrels to form a perfect example of robust masonry construction, where every block is not just doing its job but is seen to be doing its job in a most reassuring manner. It is possible to ponder these stones for hours without getting in the least bored, wondering at the creation of poetic beauty through purely expressed function.

The sight of the aqueduct entering the town – a seemingly endless arcade of granite with the conduit perched high on the immensely tall and seemingly impossibly slender piers of the lower arcade – is among the greatest surviving urban scenes from the ancient world. It was dedicated to Hercules – the legendary founder of the city – and still seems the work of divine heroes. Goodness knows what the local people felt 2,000 years ago; this mighty work is the power of Rome personified – remorseless and eternal.

The Puente de Alcántara makes a telling contrast with the cyclopean Pont du Gard and Segovia aqueduct so that, together, they encompass the whole spectrum of Roman bridge building. In comparison to the massiveness of the latter two, the Puente de Alcántara possesses a lightness of touch as it springs across the void that it was created to tame. It is, in its daring elegance, the very epitome of engineered architecture.

The Puente de Alcántara is, arguably, the greatest of all Roman bridges. It doesn’t have the widest span (that distinction belongs to the delicate first century BC Pont-Saint-Martin in the Aosta Valley, Italy whose central arch leaps 32 metres) but the Puente de Alcántara possesses an extraordinary harmony in its parts and – as with all great bridges – astonishes in its daring ambition. It is a monument to man’s ability to tackle – and to solve in an elegant manner – the most daunting of structural problems. It rises 52 metres above the bed of the river, its two wide central arches have spans of 28.3 metres and 27.4 metres and its mighty piers – made of granite from a quarry over five miles away and laid without mortar – are each nine metres square, with some of the stones weighing 8 tonnes each.

The triumphal arch in the centre of the Puente de Alcántara, bearing a panel that proclaims the bridge was built in the fifth year of the reign of Emperor Trajan - so in around AD 103.

Like the Pont du Gard, this is indeed a mighty work of man that nature has assailed in vain. All here possesses a sublime and sculptural beauty, there are virtually no classical mouldings used in its design, no details or forms superfluous to function. But the bridge is not simply a structurally supreme but spiritually arid utilitarian structure. It also possesses those details, ornamental and symbolic, that are purely poetic and that transform a great functional work into architecture. And most of these details have to do with the human story of the bridge, and its strategic function in the Roman Empire. At one level the bridge is a monument to the man who made it, and to the Emperor who ordered its construction. In the centre of the bridge is an arch, called by some a ‘fortified gate’ and by others a ‘triumphal arch’. Both definitions are correct because it is both of these things, just as the bridge is both a triumph over nature and a key military installation. The arch made the bridge defensible, or rather made it possible for those who controlled the arch to stop the bridge from being used. Whoever held the arch controlled the road that the bridge gave purpose to. But an inscription on the arch also proclaims – in triumphal manner – that the bridge was built by Emperor Trajan in the fifth year of his reign, dating it to AD 103. The man who actually built the bridge gets a smaller shrine but a far more moving inscription. Opposite one end of the bridge survives a small votive temple, a place in which the god of the river, the valley – of the bridge – would have been venerated. It carries an inscription on a marble slab:

The Puente de Alcántara, Spain, built around AD 103: its dramatic setting demonstrates the heroic and poetic beauty of Roman engineering. On the right hand side is the small votive temple where the god of the river is appeased and where, perhaps, lies buried Caius Julius Lacer, the engineer of the bridge.

‘IMP.NERVAE TRAIANO CAESARI

AVGVSTO GERMAMICO.DACIO.SACRVM PONTEM.

PERPETVI MANSVRVM IN.SAECVLA.MVNDI.

FECIT.DIVINA.NOBILIS.ARTE.LACER.

‘I …. Caius Julius Lacer ….

have built a bridge which will remain forever.’

And remain it has. Indeed the bridge is so elemental a form that it became part of the very landscape and imagination of the succeeding generations that inhabited the region. For centuries after the fall of Rome, the Puente de Alcántara was abandoned – forlorn, desolate, unmaintained – but nonetheless it stood and it was used. When the Moors came to the north of Spain they saw it, they marvelled, and they named it Al Kántarah, literally meaning ‘the bridge’. This is the defining bridge: there can be no rival. But the Moors’ admiration did not stop them breaking one of the smaller arches in 1214 during their fighting with Christian forces, nor did its antiquity and beauty stop French troops demolishing one of the main arches in 1812 when retreating from Wellington’s army. Fortunately, the damage was repaired and the bridge survives – a message from one world to another, a marvellous repository of Roman genius that continues to serve the purpose for which it was designed 1,900 years ago, that continues to glorify the road of which it forms a vital link.

Well-built roads, passable all the year round and virtually impervious to the elements, were almost holy things in the Roman world, routes of trade and cultural growth, of conquest and of defence, the veins of civilization. This high status is reflected by a small and beautiful Roman bridge, dating from the late first century BC, that by good fortune survives in the south of France. The Pont Flavien at Saint-Chamas stands astride the Via Julia Augusta – an important route begun in 13 BC on the orders of Emperor Augustus to link the commercially and strategically important cities of Placentia (now Piacenza) in northern Italy with Arles in southern France. At Arles, the Via Julia Augusta linked with the far older Via Domitia that, dating from the second century BC, was the first Roman road built through Gaul and joined Italy to Spain. Placentia was, of course, linked by road to Rome, so the Pont Flavien – with its single stone arch of modest 12-metre span – formed a small but vital link on one of the key routes from Rome, via Arles and Nîmes in southern France, to Spain. This, plus the fact that the Pont Flavien stood within the zone of the cultural, if not political, frontier between Italy and Gaul, explains its extraordinary and ambitious design. Once seen, this exquisite bridge can never be forgotten.

In its small way, the Pont Flavien is a flawless evocation of Rome, a jewel of a creation, a wonder of preservation that is a window onto a long dead world. To reach the bridge you pass along a narrow and now abandoned stretch of the Via Julia Augusta and the first glimpse you get of the bridge is a pair of stone-built triumphal arches, miniature in scale but big in meaning and magnificence. They guard each end of the bridge and offer an extraordinary perspective to all who approach. The arch in front acts as a proscenium for the one behind: very dramatic and very theatrical, and surely a visual device to let the traveller know they had arrived somewhere very special, that they were now in the frontier zone. This pair of arches, that now look uncannily like the pylons of a nineteenth century suspension bridge, were surely intended to proclaim to all travellers heading west and north that Italy was being left behind, and to those heading south that they were now entering the inner environs of the empire, drawing yet nearer on the imperial highway to Rome itself.

The stretch of road between the arches is short, narrow and now pitted and rutted, scarred by generation upon generation of chariots and carts. But despite being only a stone’s throw in length, this small stretch of road offers a vast leap into the past. To stand on this bridge at dusk is to hover in time. Here, the Rome of 2,000 years ago seems not so very distant a place, the triumphal arches being strange portals that goad the imagination. Each arch is dressed with Corinthian pilasters and carries full entablatures, the friezes of which retain handsome swirls of stone-cut acanthus. This seems celebratory, but at the corners of the arches, set above the pilaster capitals, are carved eagles, surely representing the might of Rome, and above them, carved in the round, are lions drawing back on their hind legs and about to pounce. They seem to offer a fair warning to any traveller to behave or suffer the consequences.

The modest but beautiful 1st century BC Roman bridge at Saint-Chamas, Provence-Alpes-Cote d’Azur region, France. The bridge’s importance as part of the Via Julia Augusta is proclaimed by its pair of small but perfect triumphal arches.

On the bridge is carved an inscription that appears to date from the time of construction.

It refers to Lucius Donnius Flavos, a priest from Rome in the reign of Augustus, who is described as the bridge’s builder. Builder perhaps, designer perhaps, but almost certainly the man who – as a priest – dedicated this work to the gods and called upon them to guard it. The highway was sacred and so too was this bridge: then as a gate to the Roman Empire or to Rome itself, now as an emotive and thought-provoking portal to the Roman past.

Detail of one of the triumphal arches showing the entablature with an eagle and a watchful guardian lion – surely calculated to remind travellers of the power of Rome.

CHAPTER TWO

PIETY AND POLITICS

The Pont de Valentré, Cahors, France, started in 1308. A very rare and beautiful example of a medieval bridge with fortifications intact including three towers and cutwaters containing fighting platforms and narrow windows from which passage of the river could be effectively controlled.

IN MEDIEVAL CHRISTIAN EUROPE, BRIDGES WERE built as pious works pleasing to God, as things of utility and of beauty, as part of the defence system, and of course, as routes of trade or conquest. The early fourteenth century Pont de Valentré, across the River Lot at Cahors is all of these things. I well remember, decades ago, my first glimpse one summer evening of this tall-towered, stone-built bridge. It was like something in a fairy tale: fantastic in form, pale, ethereal. The bridge adjoins Cahors, indeed formed a key part of its walled defences, but I saw it not against the town as its backdrop. It strode purposefully and elegantly across the wide and sluggish river against the background of seemingly unchanged rolling and sun-bleached countryside. It was utterly entrancing and, with its mesmerizing silhouette of tall pyramidal-topped towers and pointed arches, it seemed to sum up so many of the architectural and engineering aspirations and achievements of the age in which it was built.

The twelfth and thirteenth centuries marked the great age of masonry-built bridges in the medieval Kingdom of France and in the English possessions in Aquitaine and Gascony. In the late twelfth century, almost the entire western half of France, from the English Channel to the Pyrenees was in the possession of, or under the control of, the English King Henry II, the first monarch of the Plantagenet dynasty.

The Pont de Valentré, Cahors, France, started in 1308. A very rare and beautiful example of a medieval bridge with fortifications intact including three towers and cutwaters containing fighting platforms and narrow windows from which passage of the river could be effectively controlled.

This was a time before the modern concepts of European nationalism were forged. The Plantagenets were a branch of the French Angevin dynasty, and the English royal court was an outpost of French culture. As well as being the King of England, Henry was also the Duke of Normandy and Gascony, and Count of Anjou, Maine and Nantes. Indeed in this feudal world, popular allegiances and identity lay with the regions, rather than with the larger world or the kingdom of which the duchies or counties formed part.

The complex balance of power and land ownership in France fluctuated constantly, and by the time the bridge at Cahors was started in 1308, English possessions in the west and south had dwindled to the area around Bordeaux and to western Gascony. But the situation remained fluid, particularly during the Hundred Years War that started in 1337. During these decades of intermittent territorial and dynastic conflict, control of vast areas of the land regularly changed hands with a dramatic – if relatively short-lived – increase in English possessions in the north and northwest following Henry V’s victorious Battle of Agincourt in 1415.

The Pont de Valentré at Cahors, France, photographed in 1851, revealing its state before the restoration of the 1870s when, among other things, battlements were reinstated to the tops of the cut-waters.

Due to the wars that flared and smouldered in France, Cahors, although under French control, remained for most of the fourteenth century a more-or-less beleaguered frontier town. And the threat came not just from invasion by the English or by their French allies, but from the hordes of freebooting mercenaries and brigands that the decades of conflict and chaos in France had unleashed upon the land. So when the decision was taken to build the Pont de Valentré, it was natural that it should not only be fortified to deny passage across it to the enemies of Cahors, but also that it should be incorporated into the town’s defences. To conceive it as a barbican or redoubt would greatly enhance the military power of the town.

The designer of the Pont de Valentré, and those raising finance for its construction, would have learned well the lessons offered by other great masonry bridges constructed in southwest and central France during the previous 150 years. The most influential would have been the mighty Pont Saint-Bénezet, across the Rhône at Avignon (better known as the Pont d’Avignon, and made famous by the fifteenth-century nursery rhyme ‘Sur la Pont d’Avignon’) and the bridge over the Loire at Orléans. Both had been started within a few years of each other in the 1170s and both were seen as great works for the glory of God and the benefit of mankind.

The Pont Saint-Bénezet at Avignon had a near mythic origin that reveals the sacred nature of bridges in the medieval mind. They were seen as examples of the way in which the righteous and religious-minded could – with divine support and blessings – harness nature and command the elements. As with the Paradise Gardens of Islam (see page 118 (#litres_trial_promo)), bridges were, to medieval Christians, a means of realizing heaven on earth, of creating beauty, wealth and harmony. They were works that were pleasing to God and links not just between places on earth, but between this world and the next. In addition, bridges had an even deeper meaning for medieval Christians. In their faith, water was an important agent of transformation from the material to the spiritual. At baptism, holy water washes away sins and is part of the ritual of initiation into the Christian Church. Christ himself, perceived by Christians as the Son of God, had at his own request been baptized in the River Jordan and this action had pleased God (Matthew 13: 1–3). Given water and rivers are central to the Christian faith, so too is the means by which they are bridged.

‘Donating money towards the construction of a bridge was deemed to be a noble deed that would reduce the time that, after death, the soul would have to suffer in purgatory.’

Repeatedly in medieval France, clerics aided the construction of bridges in the same way that they aided the construction of churches and charitable institutions. In Toulouse, a testament of 1251 stated that money should be left to ‘churches and hospitals and bridges and other pious and poor places’, while in 1308, the year the bridge at Cahors was started, Pope Clement V granted for seven years an indulgence of 100 days ‘to those faithful who, truly penitent and confessed, stretched forth a helping hand to the fabric of the bridge the Dominicans were building near Nîmes’.