RPBaiao/ShutterstockOne of the amazing mysteries of Ancient Rome is the incredible longevity of some of their concrete harbor structures. Battered by sea waves for approximately 2,000 years, some survive while certain modern marine structures require major repairs after decades; performance depends on the mixture, reinforcement, exposure and engineering requirements.
A 2017 study investigated the chemistry behind this unbelievable phenomenon, and they're getting closer to unlocking its old, long-lost recipe. The studied Roman marine mixtures developed reinforcing minerals over time. This does not establish that every Roman concrete outperforms every modern concrete.
Researchers led by geologist Marie Jackson from the University of Utah have mapped Roman concrete's crystalline structure and figured out how exactly this ancient material solidifies over time.
Much modern concrete uses Portland cement, manufactured by heating calcium-rich and other mineral raw materials to produce clinker, which is then ground into cement. [source] In concrete, this paste binds 'aggregate' - chunks of rock and sand.
Engineers control aggregate composition because some reactions can damage concrete. Its service life also depends on mixture design, permeability, reinforcement and exposure; comparison with natural rock alone cannot explain its durability.
Nevertheless, Roman concrete works in a totally different way.
It was created with volcanic ash, lime, and seawater; Romans might actually have observed a similar chemical reaction in tuff rocks (naturally cemented volcanic ash deposits).
Volcanic rock aggregate was mixed into the lime-and-ash mortar, which would then keep on reacting with the material, making Roman cement far more durable than what you'd think it could be.
In a former research project led by Jackson, samples of Roman marine concrete were already gathered from various ports along the Italian coast.
Drilling for Roman concrete samples in Tuscany, 2003. Photo: J. P. Oleson
Sampling Roman concrete in Tuscany in 2003. Photograph: J. P. Oleson. Source.
The researchers mapped the samples by using an electron microscope before they examined the material to an extremely high resolution with X-ray microdiffraction and Raman spectroscopy. These advanced techniques could help them identify all the mineral grains produced in the ancient concrete over the centuries.
According to Jackson:
"We can go into the tiny natural laboratories in the concrete, map the minerals that are present, the succession of the crystals that occur, and their crystallographic properties. It's been astounding what we've been able to find."
Jackson was interested in the presence of aluminous tobermorite, a hardy silica-based mineral which is rare to find and difficult to create in the lab still is abundant in the ancient concrete.
It turned out that aluminous tobermorite, as well as a related mineral named phillipsite, grows in the concrete because of the sea water sloshing around it. The water slowly dissolves the volcanic ash within and gives it space to develop a reinforced structure by these interlocking crystals.
Making concrete, the way Romans used to once would be a boon to the modern building industry. Imagine when it comes to coastal structures, such as piers that are continually battered by the waves, or fancy tidal lagoons to harness energy from tides.
Although ancient accounts describe ingredients and methods, reconstructing the precise mixtures, processing and long-term reactions of particular structures requires archaeological and materials research.
It's not like we could replace all the world's cement with this historical stuff, since not everywhere could we access the right volcanic ingredients.
Nevertheless, if Jackson and her team can crack the recipe, contemporary marine engineers could possibly tap into the potential of a material which doesn't need steel reinforcements, could last for centuries and, also, makes fewer carbon emissions to boot.
The study was published in American Mineralogist.
Reference: Science Alert
Why Roman marine concrete attracts so much attention
Concrete combines a binding material with larger particles called aggregate. Roman builders used different mixtures for different purposes, so “Roman concrete” does not describe one universal recipe.
In a 2017 investigation led by geologist Marie Jackson, researchers examined samples from ancient Italian harbour structures. These marine mixtures included lime, volcanic material and seawater. Using microscopic and X-ray techniques, the team investigated the minerals holding the material together. Berkeley Lab’s account of the research explains what they found.
The striking feature was continued mineral growth. As seawater interacted with volcanic components, crystals including aluminous tobermorite and phillipsite developed within the concrete. Their interlocking forms helped explain how the material could resist cracking over time.
Jackson described the close-up work memorably: “We can go into the tiny natural laboratories in the concrete.” The laboratory, in this case, was partly the ancient structure itself.
The sea was part of the chemistry
It is tempting to imagine seawater as simply an enemy that an exceptionally strong wall managed to withstand. The research offers a more interesting picture: in these particular marine mixtures, water participated in reactions that created additional mineral cement.
That does not mean saltwater improves every concrete structure. A material’s response depends on its ingredients, internal structure and exposure. The lesson is to understand the system being studied, rather than turn a specific result into a rule for every building.
What Pompeii revealed in 2025
A different investigation examined an unfinished construction site preserved by the eruption of Vesuvius in 79 CE. Unlike a completed wall, this site retained raw material piles as well as structures in different stages of construction.
The 2025 study in Nature Communications identified evidence for hot mixing: quicklime was combined with dry ingredients before water was added. The resulting reaction released heat and helped explain the presence of lime-rich fragments inside the finished material.
Those fragments, often called lime clasts, are relevant to self-repair. When water enters a crack, reactive material can dissolve and contribute to new mineral deposits that fill small openings. The Pompeii evidence strengthened an earlier proposal about how such concrete was manufactured. MIT’s December 2025 explanation describes why finding unmixed ingredients mattered.
Two discoveries, with different jobs in the story
- The harbour research investigated mineral changes during long exposure to seawater.
- The Pompeii research examined evidence of manufacturing at a construction site and the behaviour of its materials.
- Together, they show why the ingredients, mixing process and later environment all deserve attention.
Neither study establishes that every surviving Roman structure used the same recipe. The Pompeii authors also discuss the need to investigate how widely the observed practices applied. That is a useful next question, not a weakness to hide.
Does this make ancient concrete better than modern concrete?
“Better” needs a job description. A harbour structure, a reinforced high-rise and a repaired masonry wall face different demands. Age alone does not give a material every property a modern engineer needs, and the buildings that survive are only part of the historical record.
The practical opportunity is to learn from the chemistry: can useful reactions make a material last longer, require fewer repairs or use resources more efficiently? The studies point toward possibilities to test, rather than a ready-made instruction to replace all modern cement with an ancient mixture.
For another example of technical skill preserved in an unexpected form, explore the Antikythera Mechanism and its astronomical gears. Both stories show how much can be learned when damaged ancient objects are examined with modern instruments.
The most impressive thing about Roman concrete may be that its history did not end when a wall was built. In the right setting, the material kept changing—and researchers are still learning to read those changes.
Additional source and image references: A researcher drills into an ancient coastal concrete structure beside the sea in Tuscany
COMMENTS