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BUILDING MATERIALS IN ANCIENT ROME
Roman bricks Unlike the Greeks who primarily built their edifices from cut and chiseled stone, the Romans used concrete (a mixture of limestone-derived mortar, gravel, sand and rubble) and fired red brick (often decorated with colored glazes) as well as marble and blocks of stone to construct their buildings.
Travertine was used to build the Colosseum and other buildings. It is a kind of yellowish or grayish white limestone formed by mineral springs, especially hot springs, and can form stalactites and stalagmites, but is also a worthy building material as the Colosseum testifies. To the untrained eye ivory-colored travertine can pass as marble. Much of it was mined near Rome in Tivoli.
Many of the buildings that were constructed during the classical period of Rome were made of soft, porous local volcanic rock called tuff that was then faced with marble. The Romans were well aware that tuff was weak especially when soaked with water or soaked with water and subjected to freezing temperatures that occasionally hit Rome. The construction method made sense in that the tuff was cheap, available, close, relatively lightweight and easy to shape. Much of it was extracted in Rome itself and covering it with sheaths marble, which was much easier and cheaper than using heavy, expensive marble blocks.
Vitruvius, the 1st century architect and engineer, wrote: “When it is time to build, the stones should be extracted two years before, not in winter but in summer; then toss them down and leave them in an open place. Whichever of these stones, in two years, is affected or damaged by weather should be thrown in with the foundations. The other ones that are not damaged by means of the trials of nature will be able to endure building above ground.”
Marble is a metamorphic rock composed of sedimentary carbonate rock, particularly limestone, that has been recrystalized as a result of extreme pressure and heat within the earth over a long period of time. When polished it gives off a beautiful shine because light rapidly penetrates the surface, giving the stone a luminous, vibrant glow. Jason Urbanus wrote in Archaeology Magazine: Researchers have gained new insight into the efficiency of Roman marble production and decoration strategies employed by Roman architects. Because marble was expensive, Romans often used thin slabs as veneers, attaching them to walls built of less valuable material such as bricks. A recent study led by Cees Passchier, a geologist at Johannes Gutenberg University Mainz, examined 54 marble panels excavated from a second-century A.D. villa in Ephesus, Turkey. Using 3-D modeling software, Passchier and his team found that 40 of the panels had been precisely cut into 0.6-inch slices from a single block of cipollino verde, a type of greenish marble known for its elaborate wavy folds, using a water-powered sawmill. The researchers determined that the slabs were not randomly hung on the walls. Instead, sections of the block cut one after the other were mounted next to each other in pairs, like opposing pages of a book. The marble’s natural patterns created kaleidoscope-like symmetrical designs. Passchier’s team also determined that the whole process, from cutting to polishing to transportation, was extremely efficient, resulting in only 5 percent of all slabs being broken, a figure on par with present-day marble production. [Source: Jason Urbanus, Archaeology Magazine, September/October 2021
Imperial Porphyry — Ancient Rome’s Most Valuable Stone
A very expensive kind marble in Roman times was called ‘imperial porphyry.’ The emperors liked it because of its deep and distinctive purple color and the fact it was very rare and hard to come by. Candida Moss wrote in the Daily Beast: All imperial porphyry mined in the ancient world came from a single, remote quarry in the eastern part of Roman Egypt called the Mons Porphyrites. It was discovered in 18 B.C. when a Roman soldier named Caius Cominius Leugas noticed a hard purple-red rock in the desert. Technically porphyry (which just means “purple” in Greek) is an igneous rock containing coarse grained crystals. Most imperial purple marble was used as an accent stone in tiled floors or on columns. You can find it fashioned into vases or busts, but the basin from Nero’s Golden House is exceptionally large and heavy. It’s almost certainly the largest single intact piece of porphyry marble that exists today. The mine established at Mons Pophryites was used continuously until A.D. 600, when the Romans lost control of Egypt. [Source: Candida Moss, Daily Beast, November 27, 2022]
Constantine’s Column in Istanbul (Constantinople) made of Egyptian prophyry
After it was extracted from the mines — which was no mean feat! — the material had to be transported. The journey began with a lengthy overland journey from the mine to the Nile. At Coptos, the marble boarded a ship up the river and carried on across the Mediterranean making stops along the way. The final leg of the journey, from the port of Ostia to the City of Rome also took place over land. Even for those not transporting heavy marble this was a lengthy journey that could take as long as 10 weeks. As Incunabula has put it on Twitter: “Imperial porphyry signaled not just power and prestige, but also that the Roman Empire could accomplish the near impossible: Cutting and quarrying the immensely hard rock, and transporting it 1000s of kilometerss from the Egyptian desert to Rome was an awe-inspiring feat of engineering.”
It was the expense of moving the stuff that made imperial porphyry so expensive and exclusive. Vanden Eykel told me that imperial marble is immediately recognizable because of its distinctive marble hue. It signifies wealth and status. Just as having a white alligator Hermes Birkin says that you have connections and $150,000 to burn on a handbag, porphyry marble signaled to your guests that you were someone of import. What says that more, said Vanden Eykel, than “a gargantuan porphyry bathtub?” The only other porphyry objects of similar scale were tombs and coffins: Nero, the Holy Roman Emperors, and even Napoleon all chose it for their final resting places. Napoleon had to make do with a common red marble.
Like other luxury products, imperial porphyry were regularly imitated. Rosso antico marble (also known as Marmor Taenarium), a beautiful red marble mined in the southern Peloponnese, was one such imitator. It was used, as Lorenzo Lazzarini notes, “as a substitute of the red Egyptian porphyry.” Though it is beautiful, rosso antico lacks the speckles and deep purple of the Egyptian marble. If you wanted to get the imperial porphyry look today, you might try a rosso impero instead.
How Come Rome's Grandest Monuments Are Still Standing?
Alex Fox of the BBC wrote: When it came to building big, the Romans clearly knew what they were doing. Nearly 2,000 years after the Pantheon and the Colosseum were constructed, these two enormous and technically astounding structures have withstood earthquakes, floods and military conflicts, long outlasting the empire that spawned them and becoming physical embodiments of the enduring influence of Roman culture across the globe. [Source: Alex Fox, BBC, December 20, 2021]
But how did ancient Rome accomplish such monumental, long-lasting architecture so long ago? Engineers and materials scientists are still studying Roman structures today, and they say the secret is the marriage of ingenious design with an innovative recipe for concrete, a supremely durable and adaptable material. Pouring concrete allowed Roman architects to achieve almost any shape they could imagine, limited only by their ability to construct the wooden forms necessary to mould the rocky slurry. But the arches, vaults and domes that are signatures of Roman buildings were not just flights of fancy.
The highest expressions of the Roman Empire's built environment confront modern visitors with an "engineering approach", said Renato Perucchio, a mechanical engineer at the University of Rochester in New York. "The Romans performed sophisticated analyses that led them to these designs, which were then expressed through an extremely careful construction process."
At the Colosseum, concrete isn't necessarily the star of the show but it has played an integral role in the arena's survival. The most prominent material at the Colosseum is travertine limestone, but concrete is what holds the amphitheater's many iconic archways aloft. Yet, perhaps the most significant contribution of concrete to the Colosseum's longevity is out of sight.
"You can't see it as a tourist, but the reason the Colosseum is still standing is because of its incredibly robust concrete foundation," said Marie Jackson, a geologist at the University of Utah. That concrete foundation is packed with dense, heavy lava rock aggregate and is a full 12 meters thick, she added. Without such a strong, long-lasting material at its foundation, the Colosseum would have been reduced entirely to rubble by the region's earthquakes.
Roman Concrete
One of the greatest advances the Romans made was the refinement of concrete. They didn't invent it, but they were the first to add stones to strengthen it, and the first to use a volcanic ash called pozzouli (found near Naples) that enabled the concrete to harden even underwater. Romans began using pozzolana in the 3rd century B.C. Mortar made with it hardened underwater and was widely employed in the construction of bridges, harbors, jetties and breakwaters.
casting a concrete wall
Roman concrete was the first building material to be used over extended spaces. Roman arches, domes and vaults would not have been built without it. Concrete had been invented about a thousand years before Roman times to build fortresses. The Romans were the first to use it on a large scale to make buildings. Most Roman concrete buildings had a facade of marble or plaster (most of which has disappeared today), covering the outsides of the concrete walls.
Many tend to think of the great buildings of antiquity as being constructed of marble but it was actually the use of concrete that made it possible to construct many of them. Concrete was lighter than stone which made it easier for laborers to work and also made it possible to raise the walls of building to great heights. Moreover it could be used to hold blocks or tuff and sun-dried or kiln-dried bricks together (a common building material since Mesopotamia) and it could be molded into different shapes. ["The Creators" by Daniel Boorstin]
J. Wisniewski wrote in Listverse: Modern concrete, unsurprisingly, is 10 times stronger than the ancient Roman variety. Nonetheless, Roman concrete is countless times more durable than modern mixtures. For all its brute strength, the typical concrete of today can’t withstand the elements, especially seawater. Against seawater, erosion sets in after just 50 years. Not so with the blend that the Romans used for their harbors and breakwaters — which, after almost 2,000 years of marine abuse, are still serviceable. Even outside of the water, there’s a significant difference in durability, with many recent concrete structures having been built with only about a century of service in mind. Roman concrete is also significantly more environmentally friendly, using less resources and requiring less heat. [Source J. Wisniewski, Listverse, July 21, 2014]
Modern Versus Roman Concrete
Alex Fox of the BBC wrote: Today, most concrete is made up of portland cement — a combination of silica sand, limestone, clay, chalk and other minerals that is baked around 2,000C and crushed into fine powder — and pieces of rock or sand called aggregate. Mixing the rocky aggregate, which varies in size from sand to gravel to small chunks of stone, with the cement makes the resulting concrete stronger and saves cement. Finally, adding water to the concrete mix sets off a chemical reaction in the cement that binds these elements together. For the most part, aggregate in modern concrete is carefully chosen to be as chemically inert as possible. The idea is to avoid any unwanted chemistry once this initial reaction concludes, since any additional reactions down the road usually crack or otherwise weaken the concrete. [Source: Alex Fox, BBC, December 20, 2021]
Roman concrete, on the other hand, is a simpler mix of quicklime made from baking and crushing limestone rocks and, most importantly, volcanic rock aggregates of various types, which were abundant in the region surrounding Rome. In contrast to the aggregates used in modern concrete, these volcanic materials used by the Romans are highly reactive and the resulting concrete remains chemically active for centuries after it first hardens.
"Portland cements nowadays are not meant to change chemically, and if they do change it's usually going to have a bad effect," said Marie Jackson, a geologist at the University of Utah who has been studying Roman concrete for decades. "Romans wanted their concrete to react. They chose an aggregate that would continue to participate in the concrete processes over time."
In contrast to modern concrete, this ongoing reactivity allows Roman concrete to get stronger over time. These long-term chemical reactions can serve to reinforce small cracks that often form between the pieces of aggregate and the binding cement and prevent them from propagating farther. This regenerative capacity, made possible by the reactive volcanic minerals, is what enables Roman concrete's tremendous capacity to endure.
Modern concrete construction might last 100 years with maintenance, but some Roman structures have survived for 1,000 years or more essentially unassisted "Sure, we can produce concrete with greater tensile strength today, but so what?" said Perucchio. "Modern concrete construction might last 100 years with maintenance, but some Roman structures have survived for 1,000 years or more essentially unassisted."
Composition of Roman Concrete
Roman concrete was made from volcanic ash, lime, water and fragments of brick and stones added for strength and color. Jason Urbanus wrote in Archaeology magazine: Modern scientists have long been baffled by the remarkable durability and water-resistant nature of Roman concrete, even after it has been submerged for 2,000 years. Although the exact recipe is lost, the base ingredients of Roman concrete are volcanic ash, lime, and volcanic rock. A new study suggests that when seawater encounters the volcanic material, it causes a chemical reaction that produces a rare crystalline mineral that subsequently reinforces the structure. Therefore, while modern concrete deteriorates quickly in water, Roman concrete actually strengthens over time. [Source:Jason Urbanus, Archaeology magazine, September-October 2017]
Pantheon, made largely of concrete
J. Wisniewski wrote in Listverse: Mineral analysis reveals that Roman builders used an admixture of volcanic ash. Not just any volcanic ash will do, though, and the Romans knew it. Under Emperor Augustus, concrete production was standardized, and concrete was mixed with volcanic ash from carefully chosen deposits.As the Romans built large and enduring structures all over the Mediterranean, they shipped thousands of tons of this volcanic ash to their far-flung builders. And now, thanks to mineral analysis of samples of Roman construction, researchers know the composition of this ash and are unraveling the mechanisms by which this pozzolan ash reacts with saltwater to enhance the resistance of Roman concrete to erosion. [Source J. Wisniewski, Listverse, July 21, 2014]
Maddie Burakoff of Associated Press wrote: Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and grinding them up. That cement is mixed with water to create a chemically reactive paste. Then, chunks of material like rock and gravel are added, and the cement paste binds them into a concrete mass. According to records from ancient architects like Vitruvius, the Roman process was similar. The ancient builders mixed materials like burnt limestone and volcanic sand with water and gravel, creating chemical reactions to bind everything together. [Source: Maddie Burakoff, Associated Press, October 3, 2023]
Marie Jackson, a geologist at the University of Utah, has found that the key could be in the specific volcanic materials used by the Romans. The builders would gather volcanic rocks left behind after eruptions to mix into their concrete. This naturally reactive material changes over time as it interacts with the elements, Jackson said, allowing it to seal cracks that develop. The ability to keep adapting over time “is truly the genius of the material,” Jackson said. “The concrete was so well designed that it sustains itself.”
Today’s builders can’t just copy the ancient recipes. Even though Roman concrete lasted a long time, it couldn't hold up heavy loads: “You couldn’t build a modern skyscraper with Roman concrete,” John Oleson, an archaeologist at the University of Victoria in Canada, said. “It would collapse when you got to the third story.”
Instead, researchers are trying to take some of the ancient material’s specialties and add them into modern mixes. MIT's Admir Masic is part of a startup that is trying to build new projects using Roman-inspired, “self-healing” concrete )See Below). And Jackson is working with the Army Corps of Engineers to design concrete structures that can hold up well in seawater — like the ones in Roman ports — to help protect coastlines from sea level rise. We don’t need to make things last quite as long as the Romans did to have an impact, Masic said. If we add 50 or 100 years to concrete’s lifespan, “we will require less demolition, less maintenance and less material in the long run.”
Self-Healing Roman Concrete
Scientists have long wondered what gave Roman concrete its incredible strength. Marianne Guenot wrote in Business Insider: The question has long puzzled scientists, not only because the concrete has incredible strength, but also because it seems to be able to self-heal — meaning cracks inexplicably disappear over time. The Pantheon in Rome is a perfect example of this. The structure, built around AD 126, has been in constant use since then. But its intricate dome looks brand new even today. So what made this material so special? A group of scientists from MIT and Harvard, who published their results in the peer-reviewed journal Science Advances on January 6, 2023 may have cracked it. These scientists suggest the secret is in white flecks found in the concrete called "lime clasts." Although these flecks are seen in pretty much every Roman structure, they have usually been dismissed as imperfections in the building material.[Source: Marianne Guenot, Business Insider, January 17, 2023]
dome of the Pantheon
Any concrete is made up of a few basic elements: a liquid binding agent, called a mortar, and aggregates (typically loose gravel, sand, or small rocks). Roman mortar was made using lime, a chemical created by heating limestone. The general belief was that the lime was first mixed with water, before adding in the aggregates. The flecks were seen as a sign the mortar was not well mixed by the builders. But Admir Masic, an author of the research and an MIT professor of civil and environmental engineering, said he was never really convinced. "If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product?" he said in a press release
After studying the flecks more closely, Masic and the team of scientists concluded that they were likely to have been put there on purpose. This, they found, was crucial to the self-healing property of the concrete. Lime clasts — the white flecks — are quite brittle, and that's a good thing. As cracks appear in the concrete, the clasts crumble, releasing calcium that can travel through the fracture. When water seeps into the cracks, the calcium, seen above in red, reacts with the water, creating new crystals. These crystals automatically fill the crack and fix the structure.
The scientists believe this could only happen if the lime was added to the concrete in its heated, powdered form. Right after it is heated in the kiln, lime is very reactive and can be dangerous. It is extremely dehydrated at this point. So as soon as this chemical comes into contact with water, it incorporates it into its chemical structure to make a more stable molecule. That reaction releases a lot of energy, which releases intense heat.
When people make concrete, they usually add water to the powdered lime first, let it cool down, then add the aggregates. But by mixing the lime with the aggregates, then adding water, the Romans created a controlled explosion, raising the heat in the mix just enough to change the concrete's chemical composition, which led to the incorporation of the lime clasts, Masic said.
The scientists put their theory to the test. They made up concrete blocks, one using the powdered lime and one using a more modern version of the concrete that did not. Then, they deliberately smashed the blocks to create cracks. They found that the Roman formulation was repaired within a couple of weeks under a drizzle of water. The modern formulation did not.
Roman underwater concrete at Caesarea harbour in present-day Israel
Roman Marble For Sale
"A profitable but uncelebrated byproduct of the grandeur of ancient Rome," Boorstin wrote, "was the medieval trade in building materials...For at least ten centuries Roman marble cutters made a business of excavating ruins, dismantling ancient buildings, and digging up pavements to find new models for their own work...About 1150...a group...even created a new mosaic style from the fragments...The medieval Roman limeburners prospered by making cement from the fragments of dismantled temples, baths, theaters, and palaces." Scavenging old marble was much easier than cutting new marble in Carrara and transporting it to Rome. ["The Creators" by Daniel Boorstin]
The Vatican often received a good chunk of the profits, until finally Pope Paul II (1468-1540) brought an end to the practice by reinstating the death penalty for anyone destroying such monuments. "Marble cutters in their own way continued the more violent and more notorious sack of Rome committed by the Goths in 410, the Vandals 455, the Saracens in 846 and the Normans in 1084." ["The Creators" by Daniel Boorstin]
Image Sources: Wikimedia Commons, The Louvre, The British Museum
Text Sources: Internet Ancient History Sourcebook: Rome sourcebooks.fordham.edu ; Internet Ancient History Sourcebook: Late Antiquity sourcebooks.fordham.edu ; “Outlines of Roman History” by William C. Morey, Ph.D., D.C.L. New York, American Book Company (1901) ; “The Private Life of the Romans” by Harold Whetstone Johnston, Revised by Mary Johnston, Scott, Foresman and Company (1903, 1932); BBC Ancient Rome bbc.co.uk/history/ ; Project Gutenberg gutenberg.org ; Metropolitan Museum of Art, National Geographic, Smithsonian magazine, New York Times, Washington Post, Los Angeles Times, Live Science, Discover magazine, Archaeology magazine, Reuters, Associated Press, The Guardian, AFP, The New Yorker, Wikipedia, Encyclopædia Britannica, Encyclopedia.com and various other books, websites and publications.
Last updated November 2024