Ancient concrete works

On April 12, 2011, in concurrence with an exhibition in the Oxford's Ashmolean Museum of some ancient treasures of Greece, the BBC announced that Macedonians created cement three centuries before the Romans [1]. Unearthing some tombs of a royal complex belonging to Alexander the Great and his father Philip, at Vergina, archaeologists determined that Macedonians were "not only great warriors but revolutionary builders as well", since they used concrete before the Romans. This information is quite interesting because shows the location of an early use of concrete. Unfortunately, if we want to shed light on the origin of the material, this simple comparison between Macedonian and Roman concretes is a little bit misleading. Moreover, it is raising another question: were Macedonians the first people using concrete? The answer is negative. Concrete was older even than Alexander the Great. Let me show you how we can deduce this fact from some Latin essays and their English translations and from the reports of Schliemann's excavations of Mycenaean archaeological sites.

First, let us remember what concrete is. It is prepared by the hardening of cement and aggregate. The cement is a binder or mortar, which is a substance that sets when mixed with water and then hardens binding together the particles of aggregate. The aggregate could be made of pebbles, ceramic tiles and brick rubbles obtained from the demolition of buildings. It is commonly believed that the ancient Romans were the first to create and use concrete. This is not true, as we can easily learn from the Latin literature itself. For sure, Romans were able to prepare high-quality hydraulic cements, because they used lime and pozzolana, the volcanic dust of Puteoli. The mixture of pozzolana and lime produces a hydraulic binder. The Romans called this binder “caementum”. “Opus caementicium” was the Roman concrete. The Roman caementum has much in common with its modern counterpart, the Portland cement: that is, the composition of Roman pozzolana cements is very close to that of modern cement. Probably, it was during the third century BC that hydraulic cement was first prepared by mixing pozzolana with the lime produced by heating limestone [2,3]. The resulting concrete was used for building the harbour at Puteoli (c.199 BC). Let me remember that Puteoli (Pozzuoli), such as Cumae and Naples, before being Roman towns, were Greek colonies of Magna Graecia. May be, the use of concrete could had come from Greece in Italy through these colonies, and, due to the local presence of pozzolana, the hydraulic cement developed and used there, and then, in all the Roman Empire. To the author’s knowledge, caementum was the only ancient material similar to the modern Portland cement. It would be interesting to analyse the compositions of Macedonian and Roman concretes to compare their features.

Early information on the properties of caementum appeared in the books written by Vitruvius and Pliny the Elder [4][5][6]. Vitruvius devoted a chapter of his book, De Architectura, to pozzolana. Pliny in his Natural History described pozzolana too, but also other concretes had been known in Rome. One was the opus signinum [7], which is obtained from broken pottery, “beaten to powder, and tempered with lime, it becomes more solid and durable than other substances of a similar nature; forming the cement known as the “signine” composition, so extensively employed for even making the pavements of houses”. Pliny considered also the “formaceos walls” that can be found in Africa and Spain. He is telling: “they are moulded, rather than built, by enclosing earth within a frame of boards, constructed on either side”. For Pliny, “these walls are superior in solidity to any cement. Even at this day, Spain still beholds watch-towers that were erected by Hannibal, and turrets of earth placed on the very summits of her mountains”. Even if Pliny is telling that formaceos walls are of “earth”, he is probably referring to the tapias [8][9][10], created with a mixture of lime, sand and gravel, that is, with a mixture for concrete. There is another reference to formaceos walls in a book on the “Rerum Rusticarum” written by Varro, reinforcing the hypothesis of concrete [11,12]. When Varro is discussing the fences used to mark the farm boundaries, he tells that fences can be masonry works too. “There are usually four varieties: those of cut stone, as in the country around Tusculum; those of burned brick, as in Gaul; those of unburned brick as in the Sabine country; those of gravel concrete, as in Spain and about Tarentum”. Varro does not describe the components of the mortar.

Of the English translation of the Varro’s book [12], the footnotes are quite remarkable. Who translated and wrote the notes was Fairfax Harrison (1869Harrison ( -1938)), American lawyer, businessman and writer. In 1913, he became president of the Southern Railway Company. Interesting person: he was an industrialist as well as the wri

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