There has always been speculation about the technological prowess of ancient civilisations, and whether they were more advanced than is generally believed. The evidence is often fragmentary and controversial – a scrap of corroded alloy, or the remains of an ambiguous artefact, like the Baghdad battery 1 and the Antikythera mechanism. 2 But in one case the evidence is solid, substantial – and if one researcher is correct – gigantic.

The term ‘cement’ dates back to the Latin ‘cæmentium’, meaning rough stone. The Romans found that crushed rock mixed with burnt lime and water formed a mixture which hardened to a stone-like consistency. It was an invaluable construction material, and there are many buildings from the Roman era made (partially) with this cement that are still standing today, including the Pantheon and Colosseum (Flavian Amphitheatre) in Rome. (Technically this is ‘hydraulic cement’ because of the hardening action of water in forming it; mud and clay were used in early cements, but these are non-hydraulic and quickly worn down by water). Cement mixed with more stone is concrete and can be used for making building blocks.

Different recipes for cement were discovered independently by the Mesopotamians, Egyptians and Romans. For some reason, the technique kept getting lost – perhaps because of stonemasons’ desire to protect their trade secrets – and the method of producing high-quality mortar was not discovered again in Europe until the 14th century. Modern cement owes a great deal to the chemists of the 18th and 19th centuries. Many great Victorian buildings, including the Houses of Parliament, were made with Portland cement, which was patented in 1824 and is still the basis for most modern cement and concrete. 3

But while the Roman buildings have endured 2,000 years or more, modern cement does not survive so well. Modern concrete can decay dangerously within decades. The problem was particularly significant in the Eastern bloc, where planners had seized on concrete as the ideal material to rebuild cities shattered by the war.

In 1957, Ukrainian scientist Victor Glukhovsky investigated why the ancient recipes were so much more durable than modern ones. From the earliest times, various additives were found to make a difference, and the ancients seem to have tried just about everything. The Romans are known to have used animal fat and milk, and more gruesomely, blood. Modern research has found that the blood altered the texture of the cement and introduced air bubbles, which help it to withstand the effects of freezing and thawing. It would be interesting to know whether the practice of making an animal or human blood sacrifice when laying the foundations of a new building is related to this. The tradition of foundation sacrifices is known across Europe, Asia and North Africa. 4

Glukhovsky discovered that superior cement could be obtained by mixing alkaline activators based on sodium and potassium, which occur in many natural minerals. His findings were quickly taken up in the Ukraine, but attracted little attention elsewhere. However, his work was important in inspiring Joseph Davidovits, a French chemical engineer. Davidovits developed a theory that the Egyptian pyramids were not constructed by assembling stone blocks as had always been assumed, but that the blocks were a type of artificial stone, made using reconstituted limestone, which had been cast in place. 5

If correct, Davidovits’s theory would solve a number of mysteries concerning the building of the pyramids. Small barrels of liquid concrete would be much easier to move than multi-ton stone blocks, and the casting process would explain how some of the blocks fit together so precisely. It would also remove the need to explain how the Egyptians worked huge quantities of stone using just stone and copper tools. This theory would require the Egyptians to be capable of manufacturing a material that is every bit as strong and resilient as natural limestone, capable of withstanding over 4,000 years of weathering. In other words, far better than any modern cement. Davidovits set out to re-create such a material. The startling thing is that he succeeded.

In 1979, Davidovits discovered a new class of materials known as geopolymers, which are similar to Glukhovsky’s building cements and have aluminosilicate mineral powders added. Technically they are formed by condensation polymerisation and (unlike other cements) do not incorporate waters of hydration within their crystal structure. They are significantly stronger than other cements, impermeable to water, and much more durable to erosion caused by temperature change or chemical action.

Geopolymers are only very slowly being accepted into the market in spite of their obvious advantages. Other concretes have been studied in depth for many decades and their properties are well known. To the industry, geopolymers are black magic: it works but we don’t know why. As further study reveals more about their physical and chemical properties, they are likely to spread.

Of course, Davidovits may be wrong about the pyramids. Critics have pointed out the archæological evidence that large stone blocks were moved and quarried. Further, there are tool marks visible on many of the blocks that make up pyramids, which would not be consistent with the theory, as well as technical issues around how cast blocks would appear. 6 On the other hand, Davidovits’s studies point to air bubbles and other signs that at least some blocks were cast, not carved.

Davidovits was awarded the Ordre National du Mérite for his achievement, and is now President of the Geopolymer Institute. 7 While Sixties tower blocks crumble, Roman structures stand firm, and the pyramids may yet prove to be concrete evidence of the superiority of ancient technology.