Moving Large Stone Blocks in Ancient Times

In ancient times, the most colossal, bulkiest stone blocks imaginable were excavated, transported, carved, and then laid in place. The sight of these gigantic megaliths astounded visitors in the past, and even today one cannot but be dumbfounded by feats that seem to stretch human ability to, if not beyond, the limit. Up to now, however, insufficient research, and particularly fieldwork, has been carried out on the methods employed. The situation is further complicated by the fact that ancient peoples have handed down very little information on their techniques; and besides, such information as we have has often been interpreted wrongly.

The classic, much quoted, example is the fresco found in the tomb of Djehutihotep in Bercia, Egypt. Djehutihotep, who lived in c. 1900 BC, commissioned a huge statue, in sitting position, and the fresco symbolizes its transport. If we trust the artist who painted the scene and assume that the statue and the men dragging it are represented on the same scale, then the statue must have been about 7 meters tall and weighed 70 tons (if the material was limestone; if it was hard stone, then the weight could have been much greater). The monolith is being dragged along on a sled by 172 people, while an assistant is pouring a liquid, possibly oil, in front of the sled to reduce friction, I believe, although some authors have suggested that a ceremonial act was taking place (Heizer 1990). In any case, with or without the oil, it is obvious that 172 people cannot pull a weight of 70 tons, and I also think that this was obvious to the artist depicting the scene, who was simply "filling up space'' with groups of people dragging to give the idea that there were many of them, as did the artist who painted the battle scene at Kadesh found in the temple of Rameses II at Abu Simbel, where the pharaoh is seen fighting against a lot of enemy chariots. The difference is that, while nobody would try calculating the number of Hittite chariots deployed in the battle of Kadesh by counting them one by one in Ramses II's frescoes, many authors have stated that the Bercia painting demonstrates how easy it was for less than 200 men to move 70 tons of statue . . .

To start with I think it advisable to divide the problem of transporting and

Moving Large Stone
Figure A2.1: The transport of the colossal statue of Djehutihotep

erecting huge masses with human labor (though the whole scenario could easily be readjusted to fit animal traction) into three distinct categories, depending on the weight involved.

The first category—standard problems—would cover weights of up to 1015 tons. Here we are dealing with what would be standard work for well-trained, motivated, and skilled teams of laborers. This category would include the majority of the blocks for the pyramids of Giza; the stones used by the Incas in square-block walls; the Easter Island "standard'' statues (about 12 tons); the granite slabs used for the temples at Giza (up to 15 tons); almost all the megaliths of Mycenaean, Hittite, and central Italy polygonal walls; and the stones used in the great monuments of Minorca and Malta.

The second category—large problems—would include loads of up to about 90 tons. Falling into this category would be the Sarsen stones of Stonehenge, the granite slabs covering the relieving chambers of the Great Pyramid, many blocks making up the Sacsahuaman at Cusco, and the architraves of the Mycenaean tombs.

The third category—mega problems—covers loads of between 100 and 400 tons. This would include the Great Menhir and other megaliths of Carnac (350 tons), the limestone blocks used in the Khafre and Menkaure temples (up to 250 tons each), many Egyptian obelisks of the New Kingdom (between 200 and 400 tons), and several dozen blocks used in Sacsahuaman (300 tons).

There are, finally, a very few instances in which even heavier loads were transported: these include the so-called Colossi of Memnon (giant statues of the pharaoh Amenhotep III at Luxor, near the Valley of the Kings, weighing up to around 600 tons), and some of the blocks used in building the Temple of Baalbeck in the Lebanon (believed to have been built by the Romans or possibly the Phoenicians) of similar weight.

Figure A2.2: Transport of a huge Human-head Bull, from an Assyrian relief

Before proceeding, it might be sensible to try to get an idea of the modern scale involved here. An average-sized car weighs about a ton. A giraffe crane (the ones you often see in city building sites) can lift up to 15 tons, though not without difficulty. For loads of up to 90 tons, massive self-propelled telescopic cranes are used—a relatively common sight. Greater loads, however, are usually only lifted by overhead-traveling cranes (commonly yellow in color), the type often seen in the docks. Normal giraffe cranes need counterweights and self-propelled cranes need to be heavily weighted at their bases. But overhead-traveling cranes (whose load is basically "hung" from a moving girder) exploit the resistance of the girder. It follows then that this type of load is usually moved on fixed paths fitted with rails (for example, between two areas of a steelworks, or between pier and freighter). A famous example of such cranes is the pair called Samson and Goliath, in a dock in Belfast, Northern Ireland. Each crane can lift loads of up to 840 tons; thus, they would certainly be capable—but only just—of moving Memnon's Colossi for a few hundred meters.

Moving one-off extra-large loads a distance is, even today, a tricky matter that strong financial or social reasons would have to justify. A recent example of a case where the transport of an outsized load of this kind came close to failure is the Italian submarine Toti, weighing 450 tons, 46 meters long, and 4.75 meters wide. The submarine, after finishing active service in 1999, was towed by river to Cremona without any mishaps. It was then supposed to proceed by land to Milan, where it was to be displayed in the Science and Technology Museum, situated in the city center (the decision to display an instrument of war in a science museum which welcomes very young children was in itself questionable in my view, though fortunately the submarine, built in the 1950s, was never involved in any kind of combat). After long deliberation, it was decided to drop the costly Herculean task of moving the monster as it was, since there was also the risk that the road would give way under the massive weight, and so the Toti ended its career somewhat ingloriously in Milan's sewers. To transport the huge object to the final destination, the Milan City Council decided it was necessary to perform some plastic surgery, removing over 100 tons of ballast and other weight and sawing through the conning tower to remove it and make the monster more manageable. Finally, stripped of its splendor and mounted on a specially designed truck, the Toti crossed the city miraculously, with an articulated truck in the rear guard mournfully carrying the sawn-off conning tower and with the backup of a steel gantry crane belonging to the military engineers, just in case.

Let us now try to gain more of an insight into the problem by looking at the force F that is necessary to apply to a load of weight P to drag it up a ramp with friction coefficient ^ and inclination a. By doing a simple calculation of elementary physics, this formula comes out as F = cos a + sin a). In practice, however, the angles of inclination of the ramp are always very small and hence cos a can be taken equal to one and sin a approximately equal to a. Assuming that a man can move T kilograms, and letting F = NT, we can obtain the required number of men with the final formula N =(P/T) (^ + a). Thus the number of men is directly proportional to the weight to be moved and to the sum of ^ and a, which one needs to make as small as possible. To make it clearer with an example, if we assume that a man can move T = 30 kg (it should be remembered that it is not like lifting a weight just for a moment as one does in a gym, so this is a reasonable estimate) and that a method is used that reduces friction to a minimum (by pouring oil on the ramp, for example), estimating the friction coefficient to be 1/5, we obtain for transport on flat ground: N = P/150 (P in kilograms). So it takes less than 20 men to move a block of 2Vi tons (2500 kg), that is, one of the two million standard blocks used in the Great Pyramid (quite a reasonable result that shows that to solve a "category 1'' problem of, say, 15 tons, about 100 men were required on flat ground). We have to add all those who did ancillary work, such as checking the smooth running of the sleds, keeping the teams in rhythm, feeding and watering the workers, and so on. Any time it was necessary to cross an irregular terrain, the number of men pulling would have to be increased substantially (for example, on a ramp with a gradient of 1/10 we would obtain approximately N = P/100).

When the weight to be moved begins to increase appreciably, normally the size of the object in question will also increase, as will problems of finding sufficiently resistant ropes—to say nothing of the logistics of coordinating a large number of men and making enough space for pulling the object. Yet I believe that as long as the weight is kept below a certain threshold (which might be reckoned to be in the region of 80 to 100 tons), we can assume that the degree of difficulty is still proportional to the load being shifted. In other words, it is quite reasonable to suppose that our formula is still fully valid. For example, to pull one of the Stonehenge Sarsen stones weighing 50 tons, we would require about 330 men, which sounds quite plausible.

The laws of physics are indifferent to the problems of mere mortals, and hence our formula continues to be valid, in principle, for any load to be moved. If we wish to move a 300-ton block, we would need at least 2000 men. But it is not quite so simple. In fact, even if the formula says 2000 men pulling together would move the block, it does not say how to arrange a sufficient number of ropes for tugging, or how to get everyone to pull at the same time, and it takes for granted that you have enough physical space for performing the maneuver and that the block will go where you want it to rather than where it wants to.

Even with more moderate loads, a larger number of men would be needed than those predicted by the formula. For instance, we have ethnological reports on the erection of some small monoliths on the island of Sumba, Indonesia, where megalithic monuments are still being put up today, which confirm this fact. These accounts show that a whole village contributes to the erection of a monolith, with hundreds of men working together at the same time, each with his own task to carry out (families save up for years to be able to sponsor the creation of a monument in honor of a dead relative). I tend to think, therefore, that the difficulties involved in transporting excessive loads are much greater than they might appear on paper, and so I must disagree with Robert Heizer (1990), one of the acknowledged experts in the field, who stated: "If a man can complete, with the help of simple tools and techniques, a quantity X of work per day, then 100 men can complete a quantity of work equivalent to 100 X''.

To summarize, I believe it is impossible to come up with a magic formula to explain how enormously complex technical difficulties were solved in the past. The only way of really understanding it is to study each problem individually, as indeed is the case today when faced with projects of exceptional difficulty.

Interesting hints might come from those transportation and construction problems that the ancients did not solve. Think, for example, of the unfinished Moai on Easter Island, or the unfinished obelisk, an enormous monolith that cracked during the excavation stage and was abandoned in a quarry at Aswan, or the most massive monolith ever shaped by men, a block some 30 meters long weighing more than 1100 metric tons, which lies in the stone quarry of the Baalbeck temples. In other cases, however, as we have seen, the puzzle has been solved. The simplest case to consider might be that of the great Egyptian obelisks, for example, that of Thutmose III, today standing in Rome, in Piazza S. Giovanni in Laterano, which weighs approximately 420 tons.

Obelisks were excavated in wide areas in the open air on the banks of the Nile. They were hewn out of the rock by immensely patient stonecutters, who used stone hammers for this long, drawn-out work (they may also have employed wooden wedges, inserted under the blocks and then dampened with water to make them expand, though the use of this technique has been documented with certainty only in Roman times), and then dragged onto huge barges. When the Nile flood level rose sufficiently, the barges floated up and their journey could begin. With this technique, which ingeniously exploited the river and the force of gravity, the Egyptians probably managed to move not just obelisks, but also enormous blocks, such as those required for the Colossi of Memnon.

Another important example is that of the Incas. Thanks to important studies by J. Pierre Protzen (1985, 1993), we have fairly good knowledge of

Figure A2.3: The Colossi of Memnon

the techniques adopted by Incan workers when megalithic blocks of standard weight (up to 10-15 tons) were quarried and moved. Protzen successfully performed some experimental tests showing how the blocks could be carved until they fitted together perfectly, using stone hammers of various sizes. But we cannot automatically attribute the same techniques and the same solutions to the construction of the gigantic Incan walls, such as those in Sacsahuaman, in Cusco, since no modern experimental testing has ever been done with even remotely comparable weights. For instance, it is quite difficult to imagine that blocks weighing up to 300 tons could be lifted and lowered the innumerable times that would have been necessary to obtain the perfect Incan joints.

It is to be hoped that in the future a systematic analysis on the extraction and erection techniques used in the past, specifically in erecting the great megaliths, will be carried out. Any such analysis will only be successful, I believe, if as much consideration is accorded to the human aspect as to the technical aspect, using, therefore, the same approach to the past that is typical of the scientific discipline we have been dealing with in this book.

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