How was concrete invented? From Nabataean cisterns and Roman pozzolana to Smeaton, Aspdin's Portland cement, Monier's flowerpots and the reinforced concrete of the 20th century

Architecture · 4 September 2026

Concrete is a mixture of a binder that hardens chemically, sand, stones and water, and it was invented at least three times: by the builders of the Near East who burned limestone into quicklime and mixed it with sand from about 7000 BC, by the Nabataeans and then the Romans who found that adding volcanic ash to lime made a cement that set under water and grew stronger for centuries, the material of the Pantheon's dome and of harbours still standing in the sea, and by the 18th and 19th centuries, when John Smeaton rediscovered hydraulic lime for a lighthouse in 1756, Joseph Aspdin of Leeds patented "Portland cement" in 1824, and Joseph Monier, a Paris gardener, put iron mesh into concrete flowerpots in 1867 and began reinforced concrete, the material of the 20th century. Below: the ancient limes, the Roman recipe and why it lasts, the thousand-year gap, the men who made the modern cement, the iron inside it, prestressing, what concrete is and why the modern kind cracks, the records and the myths, with the Roman work in Roman roads and concrete and its finest use in who built the Pantheon.

Lime: the first binder

Burn limestone at about 900 degrees and it gives off carbon dioxide and becomes quicklime, calcium oxide; add water and it slakes, with heat, into lime putty; mix the putty with sand and let it dry and it slowly takes carbon dioxide back from the air and turns to calcium carbonate again, limestone, binding the sand into mortar. This was known by 7000 BC: lime floors at Yiftahel in Israel and Çatalhöyük in Turkey, lime plaster on the walls of Jericho, and by 3000 BC lime and gypsum mortar in the pyramids, where the mortar between the blocks is gypsum burned at a low temperature because Egypt had little wood. Lime mortar hardens slowly, in air only, and is weak, and it is not concrete, which needs a binder that hardens by reacting with water; but every later cement is lime with something added. Concrete.

The Nabataeans and the Romans

The first hydraulic concrete, which sets under water, is found in the cisterns and floors of the Nabataeans in the deserts of Syria and Jordan from about 700 BC: they had discovered that lime mixed with a fine volcanic ash reacts with water into a hard, waterproof mass, and they kept their desert kingdom alive with it, in tanks that held the winter rain. The Greeks used a volcanic earth from Santorini in the same way at Rhodes and Delos in the 3rd century BC, and the Romans learned it, from the Greeks of Campania or on their own, at Puteoli near Naples, whose ash, pozzolana, gave the material its name; Vitruvius in 25 BC describes it as a powder that "produces astonishing results" when mixed with lime and rubble, setting under water and in the sea. Roman concrete, opus caementicium, was not poured but laid: a mortar of lime and pozzolana was packed in courses by hand around fist-sized stones, the caementa, between facings of stone or brick, and the mass hardened into a rock stronger than the facing; with it the Romans built from about 150 BC the harbour of Caesarea in the open sea, the Colosseum's vaults, the baths of Caracalla and the Pantheon's dome, and it is the reason those stand. The whole story of the Roman material is in Roman roads and concrete.

Why Roman concrete lasts

The Romans' concrete has outlasted every concrete since, and the reason was found only in the 2010s and 2020s: the reaction of lime, volcanic ash and seawater forms crystals of aluminium tobermorite and phillipsite that grow through the concrete for centuries and knit it tighter as it ages, so that the harbour walls of Portus Cosanus, in the sea for 2,000 years, are stronger now than when laid; and the lime was added as quicklime, not slaked, in "hot mixing", which left small lumps of lime in the concrete that dissolve when a crack lets water in and recrystallise to fill the crack, a self-healing that Admir Masic's team at MIT showed in 2023 by cracking Roman-style concrete and watching it seal in two weeks. Modern concrete has none of this: its cement reacts once and its cracks grow. The Romans did not know why theirs worked, only that it did, and they wrote the recipe down; the recipe was not lost so much as the ash, which is found in only a few volcanic regions, and the empire that shipped it.

The thousand-year gap

After the 5th century the western builders lost the trade in pozzolana and the organisation to make concrete on a large scale, and returned to lime mortar and stone: the cathedrals are solid stone and rubble bound with lime, and their vaults stand by geometry rather than by cement; in Byzantium and the Islamic world, hydraulic mortars of crushed brick and lime, "surkhi" in India, "horasan" in Turkey, carried on the idea in a weaker form, and the Chinese used sticky-rice mortar. Concrete of the Roman kind was not made again until the 18th century, and the medieval and Renaissance engineers who read Vitruvius could not find his powder outside Italy; the material of the Pantheon was, for a thousand years, a thing that had been done and could not be repeated.

Smeaton, Parker and Aspdin: modern cement

• John Smeaton, 1756. Asked to rebuild the Eddystone lighthouse on a rock in the English Channel, Smeaton tested limes and found that limestone containing clay, when burned, gave a lime that set under water; he used it, with Italian pozzolana, in the lighthouse of 1759, wrote up his experiments in 1791, and is the first man since Rome to make hydraulic cement on purpose and to know why.
• James Parker, 1796. Patented "Roman cement", made by burning the clay-rich nodules of the Thames estuary, a fast-setting brown cement used for stucco and harbour works for fifty years; not Roman.
• Louis Vicat, 1817. A French engineer who worked out the chemistry: an artificial hydraulic lime could be made by burning a mixture of limestone and clay in proportion, which is the principle of all modern cement; he published and did not patent.
• Joseph Aspdin, 1824. A Leeds bricklayer, patented "Portland cement", a burned and ground mixture of limestone and clay, named for its resemblance when set to Portland stone, the fashionable building stone; his cement was underburned and weak, and the modern material is his son William's, who in the 1840s burned the mixture at a higher temperature until it partly melted into clinker, which he ground to a powder that set hard and reliably, and kept the temperature secret. Isaac Johnson published it in 1845.
• The rotary kiln, 1885–1900. Frederick Ransome's kiln in England and Thomas Edison's long kilns in New Jersey made clinker continuously, and by 1900 Portland cement was a commodity, with the American industry, begun in Pennsylvania's Lehigh Valley in 1871, the largest in the world by 1905.

Iron inside: reinforced concrete

Concrete is strong in compression and weak in tension, like stone, so a concrete beam cracks on its underside; iron is strong in tension, and the two together are a material that can do both. François Coignet built a house of iron-reinforced concrete in Paris in 1853, and William Wilkinson patented a reinforced floor in England in 1854; but the man credited is Joseph Monier, a Paris gardener who wanted stronger flowerpots and tubs for orange trees, made them of cement mortar over an iron mesh, and patented the idea in 1867, extending it to pipes, tanks, beams and bridges over the next decade, without understanding the mechanics, which the German engineer Gustav Wayss, who bought his patents in 1879, and Mathias Koenen worked out in 1886, putting the iron where the tension is, at the bottom of a beam and the top over a support. François Hennebique, a Belgian builder in Paris, patented in 1892 a complete system, of columns, beams and floors cast as one with steel bars and stirrups, sold it through licensed contractors across the world, and built 7,000 structures by 1902; the first reinforced-concrete skyscraper, the Ingalls Building in Cincinnati, 16 storeys, went up in 1903, Frank Lloyd Wright's Unity Temple in 1908, and by the First World War concrete was the material of factories, grain silos, bridges and the war itself. Eugène Freyssinet added prestressing in 1928, stretching the steel before the concrete set so that the beam was squeezed in advance and never went into tension, which made the long spans of the 20th century's bridges possible.

What concrete is, and why it cracks

Modern concrete is Portland cement, about 12 per cent, sand and gravel or crushed stone, about 80, and water, mixed and placed in forms, where the cement's calcium silicates react with the water over hours and days into a gel of calcium silicate hydrate that binds the stones, reaching most of its strength in 28 days; it is the most used material on earth after water, 30 billion tons a year, and its making releases about 8 per cent of the world's carbon dioxide, because burning limestone gives off CO₂ and so does the fuel. It cracks because it shrinks as it dries, because the steel inside rusts and swells when water and salt reach it, splitting the cover, and because it does not heal; a reinforced-concrete structure of the 20th century is designed for 50 to 100 years, and the Roman ones have done 2,000. The answers being tried are the Roman ones: adding fly ash, slag and volcanic materials as pozzolans, hot-mixing with quicklime for self-healing, and geopolymer cements without limestone.

The records

• Oldest concrete. Lime floors of Yiftahel, Israel, about 7000 BC; Nabataean cisterns, about 700 BC; Roman, from about 150 BC.
• Oldest standing concrete building. The Pantheon, AD 126, with the largest unreinforced concrete dome, 43.3 m.
• First modern hydraulic cement. Smeaton, 1756; Portland cement, Aspdin, 1824; clinker, William Aspdin, about 1843.
• First reinforced concrete. Coignet's house, 1853; Monier's patent, 1867; Hennebique's system, 1892; first concrete skyscraper, Ingalls Building, 1903.
• Largest concrete pour. Three Gorges Dam, 27.2 million m³, 2006; Hoover Dam, 2.48 million m³ in the dam, 1935, cooled with pipes.
• Tallest concrete building. Burj Khalifa, 828 m, 2010, a reinforced-concrete tower to 586 m with steel above.
• Strongest. Ultra-high-performance concrete of 150 to 250 megapascals, against 20 to 40 for ordinary concrete and about 10 for Roman.

Versions and theories

• The Romans invented concrete. The Nabataeans had hydraulic concrete 500 years earlier and lime mortar is 9,000 years old; the Romans made it a material of empire and built the buildings that made the world remember it.
• The recipe was lost. Vitruvius's book was copied all through the Middle Ages; what was lost was the volcanic ash and the reason it worked, and the reason was found in 2017–23.
• Roman concrete is stronger than modern. It is weaker in compression, about a quarter as strong, and lasts longer, because it heals; modern concrete is stronger and shorter-lived. Both are true.
• Aspdin invented Portland cement. Joseph patented the name and a weak version; William, his son, made the real thing and hid the method; Vicat had published the principle first.
• Monier invented reinforced concrete. He patented it for flowerpots; Coignet and Wilkinson were earlier, Wayss and Koenen understood it, and Hennebique made it an industry. The flowerpots are the story everyone tells.
• The pyramids are concrete. The theory of Joseph Davidovits since 1974, that the blocks were cast in place from limestone slurry; the quarries, the tool marks, the fossils in the blocks and the geology say they were cut. The mortar between them is gypsum.

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