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The physical incarnation of the city is an almost impossibly complex puzzle that consists of tangible elements, such as geography, architecture, and the ebb and flow of people and capital, but also imponderables: the currents of history, the passage of time, and the countless number of small human choices that leave, in the aggregate, their imprint on the cityscape.
Yet cities are also imagined and then conjured – dreamscapes rendered in wood, brick, concrete, and steel. ‘As early as the outset of the fifteenth century,’ writes Ruth Eaton, a British curator, ‘one finds indications that the city was increasingly considered as an object that could be described.’
She points to the emergence, during the early Renaissance, of drawing skills, like perspective and the depiction of schematic ground plans (da Vinci), as critical innovations in the family of technologies that inform city-building. ‘The increasing sophistication and employment of surveying and drawing instruments contributed further to the distancing between the architect and the city, while the increasing availability of paper and the introduction of printing rendered his delineations easily distributable in quantity. These developments all contributed to the depiction and objective consideration of the city,’ (Eaton 2002, 41).
However, the ambitious projection of cityscapes – whether by rulers and priests or architects and planners – is as much about assembling many prosaic components as it is about the sum of imagination plus capital plus labour. This list is long and universal – bricks, beams, pipes, nails, risers, etc. It includes architectural technologies developed in response to harsh local environments, such as the mud wall domestic compounds constructed in ancient cities in Saharan and sub-Saharan Africa. Alongside building materials, structural knowhow has shaped urban space for thousands of years, e.g., lintels, the unprepossessing length of load-bearing wood, masonry, or steel that straddles the top of a door or window frame. These modest slabs serve to transfer a wall’s weight away from the gap below, preventing collapse. They were used to construct Egypt’s great pyramids and also Stonehenge. Thousands of years later, they remain a basic architectural detail in every contemporary building, including the most modest ones.
Reinforced concrete is another example – concrete reinforced with steel or iron bars is now ubiquitous. It’s not an exaggeration to say that without rebar, the modern city would not exist.2 Concrete – made from gravel, sand, and a limestone binding agent called cement – was widely employed as a building material by the Romans. ‘The formula for Roman concrete also starts with limestone: builders burned it to produce quicklime and then added water to create a paste,’ The Smithsonian explained in 2011. ‘Next they mixed in volcanic ash – usually three parts volcanic ash to one part lime, according to the writings of Vitruvius, a first-century BCE architect and engineer. The volcanic ash reacted with the lime paste to create a durable mortar that was combined with fist-size chunks of bricks or volcanic rocks called tuff, and then packed into place to form structures like walls or vaults.’ Roman concrete was weaker than modern concrete but very durable, which accounts for the resilience of monuments like the Pantheon (Wayman 2011).
Concrete fell out of use for centuries, eclipsed by brick and wood. In the 1820s, however, a British bricklayer named Joseph Aspdin patented a powder he called ‘portland cement,’ which could bind aggregates into a durable concrete (Kirkbride 2004). About fifty years later, a California-based entrepreneur, Ernest Leslie Ransome, came up with a way of making concrete even stronger.
Ransome’s father ran a cast-stone factory (the process was used to fabricate the ornate masonry widely used in nineteenth-century architecture). Ernest, born in England in 1852 and one of nine children, went to work at the plant as a young apprentice. He moved to San Francisco in 1870, got a job in a firm called the Pacific Stone Company, and eventually set himself up as a consulting engineer. In a 2019 essay in California History Journal, historian Stephen Mikesell points out that the practice of inserting iron or steel rods into concrete was well established. What Ransome figured out, however, was that by using twisted rods, the reinforced concrete had greater tensile strength – meaning it could withstand forces that torqued structures such as bridges or columns. ‘His twisted rebar,’ Mikesell writes, ‘was a major advance in that it allowed for the use of much smaller pieces of metal, saving money and materials, particularly when the metal surface was deformed to better adhere to the concrete.’ Ransome’s rebar went into construction of the two oldest reinforced concrete bridges in the U.S. – both in Golden Gate Park – as well as numerous other buildings designed by his firm. It also paved the way for further innovation in this most basic kind of building material.
Mikesell writes that Ransome built his career in a booming port/gold-rush city – San Francisco in the late nineteenth and early twentieth centuries – that had attracted many self-taught engineers. ‘We may never again see the like of Ernest Leslie Ransome, a developer of construction methods and machines and a builder of great structures, who learned his craft through apprenticeship and by experience, not in university study’ (Mikesell 2019, 18).
It’s safe to say that very few people pause to think about rebar as they move through contemporary cities, and even fewer would be aware of someone like Ransome. But the importance of this type of city-building technology becomes highly apparent when it is missing, as happened when a forty-two-year-old Miami condo building, financed in part by Canadian investors, collapsed in the summer of 2021, killing ninety-eight people. When investigators sifted through the rubble and examined CCTV images, they realized that several rebar-reinforced columns in the main-floor parking garage showed signs not just of corrosion from salt, but also construction that didn’t meet design standards. ‘Critical places near the base of the building appeared to use less steel reinforcement than called for in the project’s original design drawings,’ the New York Times reported days after the tragedy. Quoting observations by a forensic engineer, the paper noted that ‘there were signs that the amount of steel used to connect concrete slabs below a parking deck to the building’s vertical columns might be less than what the project’s initial plans specified. ‘The bars might not be arranged like the original drawings call for’ (Glanz et al. 2021).
Beyond the building blocks and techniques that fuelled city-building, the lengthy evolution of civil engineering further reveals the deeply intertwined relationships between cities and commerce, geopolitics, and even the cosmologies that informed urban design.
As far back as the 5th century BCE, Chinese rulers commissioned the construction of a far-reaching network of canals used for agriculture and taxation (paid in grain), but also as a means of connecting rural areas to cities. Canal-building enabled the production and transportation of rice, a staple in heavily populated Chinese urban centres. According to a 1998 account of pre-industrial Chinese engineering and technology, the canal networks linking cities and rural areas fostered, or at least accelerated, the development of two other technologies: large-scale printing and iron fabrication. As technology historian Arnold Pacey explains, there was a boom in demand both for books on rice production and plowing equipment, manufactured in ironworks plants located near coal mines (Pacey 1998).
In Kaifeng, one of China’s ancient capitals situated in the country’s northeast region, canals entered the metropolis through so-called ‘water gates’ in the city walls. These formidable structures, another fixture of Chinese civil engineering, surrounded many large urban centres, tracing the edges of the rectilinear street grids inspired by Confucian cosmology and other teachings on the layout of political cities, including Beijing. The tower walls and parapets served, obviously, as a form of military defence against invaders, but, as Pacey notes, they signalled something else about urban form:
The same connection between walls, gates and orderly government is indicated by the following anecdote. Confucius is said to have been in a horse-drawn carriage with one of his disciples when he encountered some children playing in the road. The children had used loose tiles and bricks to build a model city wall across the road and, as the carriage was about to scatter these playthings, one of them stood up and asked Confucius a question: ‘Should the city wall be destroyed or ought the carriage to turn round if it cannot pass through the wall-gate?’ Confucius apparently recognized an appeal to ideals of civil order and good government and asked his driver to turn the carriage around. (298)
Basic human needs drove yet another category of early civil engineering, geared toward providing fresh water and disposing of human waste at scale. Many ancient cities relied on the provision of latrines, public baths, and drainage pipes. ‘The Romans did build many structures seemingly dedicated to improving sanitation – in addition to public toilets, they had bathhouses and sewer systems like the giant Cloaca Maxima in Rome,’ explained a 2016 feature on Roman hygiene in The Atlantic. ‘“They [also] introduced legislation so that towns had to clear away the waste from the roads and things and take all that waste mess outside towns,”’ Piers Mitchell, a University of Cambridge paleo-pathologist told the magazine, adding that his research showed such infrastructure didn’t actually prevent disease (Beck 2016).
While Romans tend to get most of the credit for early advances in civil engineering, other civilizations recognized how to leverage the underlying principles of physics to build similar infrastructure. In 2010, a team of archaeologists published remarkable findings about Palenque, a Mayan citystate in Mexico’s Chiapas region that existed from 250 to 900 CE. They uncovered evidence of a pressurized municipal water system engineered with spring-fed aqueducts and built almost a thousand years before the arrival of the Spanish conquistadors.
‘Underground water features such as aqueducts are not unusual at Palenque,’ Science Daily reported in 2010. ‘Because the Maya built the city in a constricted area in a break in an escarpment, inhabitants were unable to spread out. To make as much land available for living, the Maya at Palenque routed streams beneath plazas via aqueducts. “They were creating urban space,” said Kirk French, lecturer in anthropology at Penn State. “There are streams in the area every 300 feet or so across the whole escarpment. There is very little land to build on.”’ The archaeological evidence also showed how the aqueducts help mitigate flooding in the city (Penn State 2010). Several centuries later, in Tenochtitlan and Tlatelolco, the Aztec imperial city located 900 kilometres northwest of Palenque, generations of builders created an extraordinary feat of urban engineering and reclamation in the middle of Lake Texcoco, which once occupied part of the present-day location of Mexico City. With a population of approximately 400,000 when the brutal Spanish occupation began in 1519, Tenochtitlan and Tlatelolco had been built on reclaimed and then elevated islands, traversed by canals, with neighbourhoods and adjoining fields linked by hundreds of wooden bridges. At the time, the city – constructed over centuries and financed by an elaborate system of taxation imposed by the Aztecs on nearby regions – had about 60,000 houses built in rows along canals and radiating out from a central precinct of pyramids and temples, all of which were destroyed by the conquistadors. To the Spanish, Tenochtitlan reminded them of Venice.
According to a history of this remarkable Meso-American capital by University of Colorado, Boulder, anthropologist Gerardo Gutiérrez, ‘[t]he most extraordinary projects … were the artificial causeways connecting the island to the main cities on shore, the aqueduct that brought fresh water to the city, and the dikes that regulated the level of Lake Texcoco. All these engineering projects were formidable tasks that would have been impossible without the forced labor of the conquered polities around the lake’ (Gutiérrez 2015).
The elaborate nature of Tenochtitlan’s built form serves as a reminder that knowledge about many of the most basic elements of civil engineering did not diffuse, but rather evolved independently in many places, over many epochs, with distinctly urban impacts.
Consider the construction of permanent structures anchored in water, such as the Mnjikaning fishing weirs, located in a narrows at the north end of Lake Simcoe, in Ontario. The weirs, now a national historic site, date to about 3300 BCE and consist of clusters of wooden stakes driven into the clay of the shallow lake bottom. Indigenous fishers strung their nets between the stakes to catch fish.
Maintained over five millennia, the weirs were used in more recent times by the Huron-Wendat and later the Anishnaabeg. Nor were they designed simply to enable fishing. The weirs served as a gathering place imbued with both social and spiritual significance for Indigenous peoples in Southern Ontario and could be described as proto-urban. ‘The only other examples known to exist are in the Pacific Northwest, the Canadian North, and the State of Maine in the American Northeast,’ according to a 2003 thesis by Kate Mulligan.
Long before the advent of steel-and-concrete spans of the sort that Ernest Leslie Ransome had made possible, bridge engineers understood how to build ‘cribs’ or ‘bathtubs’ in fast-moving rivers, creating enclosures made of stones with logs affixed to the bottom. Once these cribs were reasonably watertight, labourers pumped out the enclosure and erected piers that could be securely anchored to the bottom – a technique still used in contemporary bridge construction.
Meanwhile, arched spans, with loads supported and distributed using capstones and trapezoid-shaped blocks, were strongly associated with Roman engineering. Yet similar bridges existed elsewhere, among them the Zhaozhou Bridge in Northern China. Built about 1,400 years ago, it is considered the world’s oldest spandrel stone bridge still in active use. (The structure is located in a city of half a million people called Zhao County.)
Bridges, of course, aren’t inherently urban forms of civil engineering. But these structures enabled urban development by allowing cities to expand across bodies of water, rivers, and ravines, establishing physical connections that enabled commerce, migration, new development, and transportation.
By contrast, the evolution of road-building technology follows a somewhat different trajectory. Paths and then roads are as old as human civilization. But for much of early recorded history, they were constructed from flagstones or logs – so-called corduroy roads – or simply existed as beaten ground. The Romans developed sophisticated road engineering techniques that supported an empire extending across Europe. ‘Famous for their straightness, Roman roads were composed of a graded soil foundation topped by four courses: a bedding of sand or mortar; rows of large, flat stones; a thin layer of gravel mixed with lime; and a thin surface of flint-like lava,’ according to one historical account. ‘Typically they were 3 to 5 feet thick and varied in width from 8 to 35 feet, although the average width for the main roads was from 12 to 24 feet. Their design remained the most sophisticated until the advent of modern road-building technology in the very late 18th and 19th centuries’ (Sponholtz).
While medieval cities had some paved streets, the game-changing innovation in road-building – and, simultaneously, road financing – occurred in Bristol, England, in the early 1800s. In 1806, a Scot named John Loudon McAdam, who had once worked as a coal tar manufacturer, became the paving commissioner in Bristol, a booming Atlantic port and destination for imports of sugar and tobacco from American plantations. After almost a decade, McAdam took on a post with a far broader scope, and one that would cement his legacy as the inventor of the modern paved highway.
At the time, inter-city highways, known as turnpikes, were managed by trusts and toll keepers. McAdam, who had testified before a House of Commons committee on reforming England’s roads, argued for a more professional form of administration and also spelled out design principles that road contractors and surveyors must follow. These included excavating and levelling the roadbed, packing it with layers of crushed stone and gravel, and ensuring a contoured surface that caused water to run off to the side instead of pooling. ‘Not only did John Loudon McAdam’s design result in a smoother surface and carriage ride, but it was cheaper to build and lasted longer,’ noted an essay in Interesting Engineering, an engineering blog. ‘This “new” roadway surface and construction process have since been immortalized with McAdam’s name, often with the Americanized spelling “MacAdam” or “macadam.”’ (Later innovations involved sealing the surface with tar and eventually asphalt.)
While McAdam (and his sons) had gradually gained control of turnpikes around Bristol, he and other reformers pressed the British government to centralize authority over the country’s transportation network, as well as London’s metropolitan system. McAdam, who wrote several books about highways and turnpikes, argued that the government should hire surveyors and dispatch inspectors, and allocate revenues specifically for road maintenance. He had public opinion on his side, as travellers complained about the combination of terrible road conditions and high tolls, which were especially prevalent around London.
By the end of his life, McAdam had become not only internationally renowned, but also a verb. ‘“Macadamizing” was not only, in its literal sense, a practical work of great public utility,’ commented a prominent British historian. ‘[I]t became a symbol of all progress, and was metaphorically used in common parlance for any aspects of the new age where improved and uniform scientific methods were in demand’ (Spiro Jr. 1956, 212).
2. Rebar, of course, is not just used in cities, but cities amplify the importance of such basic materials.