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.28 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