Roman Cement: Genius from Roman Artisans and Engineers


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Stabian Bath

The Stabian baths of Pompeii were crafted by Roman artisans using Roman cement. The cement hardened quickly and the drying process was aided by moisture. Copyright image by Natasha Sheldon, used with permission. All rights reserved.

Ancient Roman civilization left behind numerous legacies that we still study and admire – including their amazing cement. What’s the secret behind the stately buildings of Roman times?

Roman Technology

Modern cement owes its origins in part to ancient Roman engineers who utilized volcanic components from Mount Vesuvius to create a unique cement that took years to ‘decode.’

The Vesuvian components make Roman cement a superior cement that rivals modern standards. The ancient Romans, perhaps, stumbled upon the use of the Vesuvian component to cement while quarrying for its components, clay, gypsum, and lime.

Cement is an ‘earthen product’ – it’s quarried from the ground. Cement’s true origins result from humanity’s need for safety and shelter. Simple components from the ground, when heated and mixed with sufficient water, will harden to be impervious to most weather events. How did Roman cement remain superior to modern engineering standards until the early-1800s?

Roman Cement: What is it?

Roman cement, a unique formulation of lime, gypsum, sand, gravel, and pyroclastic fly ash from Mt. Vesuvius, was a superior cement for almost two millennia. In order to make a superior cement, the Romans heated the lime-gypsum mixtures (to drive away carbon dioxide) and utilize pyroclastic fly ash of Mt. Vesuvius. Then, artisans thoroughly mixed the heated components with gravel, water, and sand.

What made the resultant Calcium and Aluminum components (from the lime and gypsum, respectively) important are their ability to selectively bind to Silicates in the fly ash thus making a superior mortar to bind cement. These formulations have seen multiple ancient structures left standing to the present day.

Magnificent structures including the Pantheon, most of Pompeii and Herculaneum, as well as numerous converted Basilicas, and Cathedrals reveal the ‘Roman touch’ to their construction.  Perhaps the most telling aspect of Roman cement comes from its similarity to 20th century cement. The replacement to Roman cement came after centuries of inferior replacements that could not match the lost formulations of the original.

How the Formulation of Roman Cement Became Lost

Because Roman cement was quarried, initial understanding of cement was qualitative. We didn’t figure out the scientific laws that explain how chemical components formed in proportion to their physical properties until more than 1500 years after the formulations of Roman cement were lost. What happened? The Dark Ages.

Once the Dark Ages fell upon Western society, all things Roman would not be revived until after the European Renaissance. However, even then, the engineering feat of Roman cement seemed to be more art than science. And much like the Alchemy of the Dark Ages, technologists were concerned with transmuting common gravel into ‘gold’ or finding the philosopher’s stone that could enable such transmutations. The formulation for cement became fodder for the nefarious seeking profit.

Distinguishing Characteristics of Roman Cement

Roman cement was special. Structures like the Pantheon and Roman Coloseum stood strong for more than a thousand years despite little or no upkeep. Cement used at or near the salt water of the Mediterranean stood strong, as well – the cement of the Roman period grew stronger for a time after setting. Another distinguishing fact of Roman cement was its ‘hydraulic nature’ –it could set and harden under water.

While the cement that was made in Europe during the 16th, 17th,  and 18th centuries retained some of the characteristics that made it similar to Roman cement, engineers and technologists did not understand the certain aspects that made Roman cement important.

The fly ash of Mount Vesuvius made the Roman cement impervious to weathering, and the skilled artisan quality with which engineers made the cement was another aspect that made Roman cement outstanding. It looked like art, but that high quality manufacture was, in truth, a science.


Roman cement was crafted by skilled artisans whose expertise rivaled present day methods. Copyright image by John A. Jaksich. All rights reserved.

Roman Cement: Calcium-Silicon-Aluminum and Twelve Other Elements

The original recipe for the cement came from the ancient Greeks—who had constructed important, long-lasting monuments and buildings, as well. The ancient Romans, perhaps, stumbled upon the Vesuvian component to cement while quarrying for the base components of clay, gypsum, and lime.

The importance of the Vesuvian components can be seen in modern chemical analysis of the fly ash. When chemists analyze the fly ash of Mount Vesuvius, the results are somewhat curious and reveal the nature of Roman cement’s effectiveness.

The major components: silicon, aluminum, and calcium form an interlocking network when in presence of the Vesuvian components. Interestingly enough, however, there are at least 12 other separate molecules within the fly ash of Vesuvius. The molecules are primarily oxidized metals with phosphates, sulfates, in a watery, acidic mixture. Although, at first glance, it appears to be a smelly, acidic mixture—once in contact with the proper ratio of silicon, aluminum and calcium, the mixture will harden.

Creating Granite

The process by which the cement forms is when the clay, gypsum, and lime are heated and the other components attach to the heated components in enough water for solidification. It is almost as if one were re-forming  granite from scratch.

Roman artisans and engineers were decades ahead for their time period. The genius of their skills was realized by knowing that necessity was the true ‘mother of invention’ – and genius, for both art and science.

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