One of Our Greatest Inventions: The Beauty of the Brick
Engineer Roma Agrawal Delves Into the Science of Materials
I love baking, which is perhaps not surprising, given that it has a lot in common with engineering. I like the way you have to follow an ordered series of processes to construct a cake. I like that you work in a very patient and precise fashion, otherwise you won’t get the right shape and texture. I like the hopeful wait, that quiet period when my work is done and it slowly takes shape in the oven. Usually, I find all this incredibly satisfying. But there are moments of perplexed frustration—like the time I opened the oven door ready to slide out a delicious pineapple upside-down cake and was confronted instead with chunks of uncooked fruit swimming listlessly in a greasy sea of butter. Forget soggy bottom, this was a soggy disaster. Cursing the oven and recipe (after all, it could hardly have been my fault), I slung it straight in the bin: useless—except as a valuable reminder that in baking, as in engineering, the right choice of materials, combined in the correct way, is crucial to the outcome.
When designing a building or bridge, materials are one of my foremost concerns. In fact, different materials can entirely change the way the frame of a structure is arranged, how intrusive it feels, and how physically heavy and expensive it is. They must serve the purpose of the building or bridge correctly: I need to weave in the skeleton of the structure without it becoming obtrusive to the people using it. The materials must also resist the stresses and strains of loads that assail a building, and perform well in the face of movement and temperature fluctuations. Ultimately, my choice of material has to ensure that the structure survives as long as possible in its environment. Luckily, my engineering creations are more successful than my baking endeavors.
The science of materials has long obsessed humans, and since ancient times we have theorized about what makes up “stuff.” The Greek philosopher Thales (c. 600 BC) contended that Water was the primordial substance of all things. Heraclitus of Ephesus (c. 535 BC) said it was Fire. Democritus (c. 460 BC) and his follower Epicurus suggested it was the “indivisibles”: the precursors to what we now call atoms. In Hinduism, the four elements—earth, fire, water and air—described matter, and a fifth—akasha—encompassed that beyond the material world. Roman engineer Vitruvius writes in De Architectura agreeing that matter is made up of the same four elements, adding that the behavior and character of a material depends on the proportions of these elements within it.
This idea—that there were a limited number of fundamental ingredients which in different proportions could explain every color, texture, strength and other property of any material—was revolutionary. The Romans surmised that materials which were soft must have a larger proportion of air, and that tougher materials had more earth. Water in large proportions made a material resistant to it, and brittle materials were ruled by fire.
Ever curious and inventive, the Romans manipulated these materials to better their properties, which is how they made their renowned concrete. They may not have had the periodic table (it would be a while before Dmitri Mendeleev published the original version of the table in 1869), but they knew that the properties of a material depended on the proportions of its elements, and they could be changed by exposing it to other elements.
For a long time, however, humans simply built from the materials that Nature provided, without changing their fundamental properties. Our ancient ancestors’ dwellings were made from whatever they could find in their immediate surroundings: materials that were readily available and could be easily assembled into different shapes. With a few simple tools, trees could be felled and logs joined to create walls, and animal skins could be tied together and suspended to form tents.
If there were no trees, humans created homes from mud. As we developed our tools and became more innovative and daring, we took this one step further—we tried to make the mud better by shaping it into rectangular cuboids of various sizes using wooden moulds. We discovered that by allowing the mud to dry in the sun (according to Roman philosophy, letting the water escape and the earth take over, using fire), the result was a much tougher unit. Humans had created the brick.
Bricks were already in use around 9000 BC in an expanse of desert in the Middle East. In the deep valley of the River Jordan, hundreds of meters below sea-level, Neolithic man created the city of Jericho. The residents of this ancient city baked hand-moulded flat pieces of clay in the sun and built homes with them in the shape of beehives. As early as 2900 BC the Indus Valley Civilization was building structures using bricks baked in kilns. It was a process that required skill and precision: if it wasn’t heated for long enough, the shaped mud wouldn’t dry out properly. Heated too much and too quickly, it would crack. But if baked at the right temperature for just the right length of time, the mud became strong and weather-resistant.
“The energy and inventiveness of Roman engineering is, for me, a source of wonder and inspiration.“
Archaeological remains from the Indus Valley Civilization have been found in the ruins of Mohenjo-daro and Harappa, in modern-day Pakistan. Every brick they used, no matter what its size, was in the perfect ratio of 4 : 2 : 1 (length : width : height)—a ratio that engineers still (more or less) use, because it allows the brick to dry uniformly, it’s a handy size to work with, and it has a good proportion of surface area that can be bound to other bricks with whatever form of glue or mortar is used. At about the same time as the Indus Valley Civilization, the Chinese were also manufacturing bricks on a large scale. But for the humble brick to become one of Western civilization’s most used materials, we had to wait for the rise of one of its greatest empires.
The energy and inventiveness of Roman engineering is, for me, a source of wonder and inspiration. So it was with not a little excitement that I took a train south from Naples, along the coast, to one of the most famous archaeological sites in the world. Wearing matching sandals, my husband and I alighted at our destination and put on matching safari hats to keep the scorching summer sun at bay. In great anticipation, we strode towards the ancient ruins of Pompeii.
Along the cobbled streets were shopfronts with counters studded with holes in which conical pots or amphorae were once stored. On the ground was a dramatic floor mosaic of writhing fish and sea creatures. Another showed a ferocious canine and was inscribed with the legend “Cave canem”—”Beware of the dog.” Alongside these were well-laid-out homes, like Menander’s (a Greek writer), with its spacious atrium, baths and garden surrounded by a beautifully proportioned colonnaded walkway or peristyle. All these gave a powerful impression of what a glorious, bustling town it must have been in its heyday.
Among the things that most caught my eye, though, were the blood-red bricks. They were everywhere. They peeked surreptitiously from columns on which the decorations that originally hid them from view had crumbled away. They looked proudly on from the walls, where they were arranged in thin layers of three, alternating with sharply contrasting layers of white stone. But my favorite brick-built features were without doubt the arches.
Arches are important building components. They are curved—they are a part of a circle or an ellipse, or even a parabola. They are strong shapes. Take, for example, an egg: if you squeeze an egg in your hand with a uniform grip, you’ll find it nearly impossible to break because the curved shell channels the uniform force of your hand around itself in compression, and the shell is strong in resisting it. To crack the shell, you normally have to use a sharp edge, such as the blade of a knife, on one side, creating a non-uniform load. When you load an arch, the force is channelled around its curved shape, putting all portions of the arch in compression. In ancient times, stone or brick were commonly used building materials—these are great under these squashing loads but not tension loads. The Romans understood both the properties of such materials and the virtues of the arch, and they realized they could bring the two things together in perfect union. Until then, flat beams were used to span distances, whether in bridges or buildings. As we saw earlier, when loaded, beams experience compression in the top and tension in the bottom—and since stone and brick aren’t very strong in tension, the beams the ancients used tended to be large and often unwieldy. This limited the length of the beams’ spans. But by using the high compression resistance of stone in an arch, the Romans could create stronger and larger structures.
The brick arches surrounding me had survived millennia, and made me think of the beautiful ancient Arabic saying “Arches never sleep.” They never sleep because their components are continuously in compression, resisting the weight they bear with endless patience. Even when Mount Vesuvius spewed lava over Pompeii, smothering its people and buildings, the arches remained the watchers of the city. They may have been buried, but they never stopped doing their job.
Roman bricks were, in general, larger and flatter than those we use today. They looked more like tiles: the Romans favored that shape because they realized that, with the tools and methods they used, flatter bricks would dry out more evenly—an essential feature of the ideal brick recipe. From the temples in the Forum in Rome to the Colosseum and the extraordinary triple stack of arches that make up the Pont du Gard aqueduct that spans the River Gardon in southern France, bricks formed the basis of their most impressive structures.
When the Roman empire fell in AD 476, the art of brickmaking was lost to the West for several hundred years, only to be revived in the Early Middle Ages (between the 6th and 10th centuries), when they were used to build castles. During the Renaissance and Baroque periods (from the 14th to the early 18th centuries), exposing bricks in buildings went out of fashion, and instead they were hidden behind intricate plaster and paintings. Personally, I like seeing bricks on display, much as I like seeing the air ducts and escalators on the outside of the Centre Pompidou. I prefer my structures direct and honest: like my cakes, I enjoy being able to view the materials from which they are created (this has nothing to do with my complete lack of icing skills).
During the Victorian period in Great Britain (1837 to 1901), and between the World Wars, the use of brick peaked to its highest in recent history. One of my favorite buildings in London, George Gilbert Scott’s grand Gothic fantasy the St Pancras Renaissance Hotel, is a spectacular example of an exposed brick structure. Up to ten billion bricks were made annually in Britain. It seemed that all structures, from factories to houses, from sewers to bridges, were made from bricks, left exposed for all to see.
This ancient building block, born from the earth and baptized by fire, is so versatile that it was used in the construction of pyramids, the Great Wall of China, the Colosseum, the medieval Castle of the Teutonic Order in Malbork, the famous dome of the Catedrale di Santa Maria del Fiore in Florence, and even my own house. I love that in our modern, fast-paced world, with all the technology we’ve developed, we continue to rely heavily on a building tool that has been in use for over 10,000 years, created from a material that was 50 million years in the making.
Adapted from the introduction to Built: The Hidden Stories Behind our Structures. Used with permission of Bloomsbury. Copyright © 2018 by Roma Agrawal.