Professor Jean-Pierre Protzen, Chairman of the Department of Architecture at the University of California at Berkeley, also found that practical experimentation can help solve some mysteries. While on a visit to central Peru in 1979, he became fascinated by the ruins of buildings constructed by the ninth emperor of the Incas.
The huge blocks of stone, some weighing well over 100 tons, were put together in a most remarkable way: each block fitted together so tightly that it was impossible in many cases even to slide a knife-blade into the joints. What was the secret of the Inca stone-masonry? Professor Protzen assumed that when he returned to Berkeley he would be able to find out from a book in the university library. But there was no book, and no one seemed to know the answer.
In 1982 the professor set out for Peru once more, determined to crack the mystery. First he examined the spectacular Inca walls at Cuzco, Saqsaywaman and Oliantaytambo. Then he visited the quarries from which the stones had been cut, marvelling in passing at the slides down which the blocks were transported from the rock face. One slide, at Kachiqhata, had ‘an awesome 40-degree slope with a 250-meter vertical drop’.
At another quarry Protzen found 250 large stones which, he realized, were ‘examples of all the stages of production, from raw stone to finely dressed blocks’. Scattered amongst them were stones which had obviously come from outside the quarry, probably from the banks of the Vilcanota River nearby. These, he decided, were hammers with which the blocks had been worked. He identified three types: the heaviest probably shaped the stones immediately after they had been cut from the main rock face; the medium-sized ones could have been used for dressing the blocks; and the edges would have been fashioned with the smallest hammers.
The time for theorizing was over. The professor chose a likely looking block and set to. With just six blows of a 9 lb (4 kilo) stone hammer, he shaped a rough block, and then, with another hammer, pounded one of its faces until it was smooth. To protect it from the impact of heavy blows to the next face, he used one of the smallest stones to draft the edges before turning the block over. Ninety minutes later, three sides were dressed. A comparison of the test block with those worked by the Incas confirmed that Professor Protzen’s hypothesis was plausible.
Now it was time to tackle the heart of the mystery. How had the Inca stonemasons managed to make the blocks fit together so tightly? The examination of ruined walls provided the clues. Joints – usually concave depressions – were cut in the lower blocks so that the upper course could fit into them precisely. The sides of each block were slotted together in the same way. Once again, Professor Protzen tried the technique himself. He took the block he had already dressed and placed it on top of another. Then he traced the outline of the upper stone upon the lower, removed the top block, and pounded away until he had hollowed out a depression for the top one to fit into. Before long, both stones were tightly locked together.
The enigma of Inca stone-masonry had yielded to an enquiring mind and an energetic arm.
The Great Glass Slab of Galilee
There are some mysteries, however, which cannot be explained by experiment or enterprise; when archaeologists have to make do with excavation and informed guesswork. In the 1950s the local authorities near Haifa, Israel, decided to build a museum in a cave at Beth She’arim, the site of an ancient city where Jews were buried in catacombs. The cave had been used as a water tank and, since it was badly silted-up, a bulldozer was brought in to clear it. In the middle of the floor, the machine struck a large slab, which the museum administrators decided to keep and use as the base of a display case. For years afterwards, visitors filed past, looking only at the model of a building laid out upon it, not realizing that the slab itself was by far the most interesting exhibit of all.
Eventually, some local archaeologists took a closer look at the slab. To their amazement, they found it was not made of rock at all, but of strange purplish-green glass. A search through the record books brought a further surprise. The slab measured 3.40 m by 1.94 m (over 10 ft by 6 ft), was about 50 cm (nearly 20 in) thick, and weighed about 8.8 tons. This made it the third largest piece of glass ever known to have been made by man, ranking only after two giant mirrors manufactured in 1934 – making full use of the current technology – for the Hale Telescope at Mount Palomar in the United States. Yet from what was known of the history of the cave, the ‘Great Glass Slab of Galilee’, as it came to be called, was well over 1,000 years old.
In 1964, soon after its discovery, a team of American experts was called in to investigate the slab. Its leader, Dr Robert Brill, Administrator of Scientific Research at the Corning Museum of Glass, New York, was mystified. The slab was certainly made of glass – laboratory tests on a core taken from it with a power-drill proved as much. But what was the third largest piece of glass in the world doing in a cave in Galilee? And who had made it, and when and why? To produce a slab that size would certainly have been a daunting task, requiring around 11 tons of raw material kept at a temperature of 1,150°C for several days.
In fact, finding out how the glass had been made did not prove difficult. Brill and his colleagues managed to excavate beneath the slab and there they found a layer of large stones which appeared to have once been covered with clay. This, Brill guessed, was the bottom of a large tank in which the glass must have been mixed and fired. He went on to suggest that firing chambers were probably built at the side to provide heat for melting the material and that the whole tank was covered over. He later learned from the archaeologists that, within living memory, a course of large stones had existed around the slab, and this strengthened his conviction that a tank had been used.
It was fairly simple, too, to guess why the slab had been left in the cave: Brill’s chemical analysis of the core showed that it had gone wrong in the furnace. At the bottom the raw materials had not fused together properly, the whole thing had crystallized – and its dull appearance meant that no one recognized it as glass when the museum was opened.
Comparisons with other ancient glass from the area – in addition to his knowledge of the history of the cave -enabled Brill to estimate that the slab had been made at some time between the fourth and early seventh centuries, but he was at a loss to explain why the glassworkers of ancient Galilee had embarked upon their laborious task in the first place. There was one clue, but it told him little.
Manganese had been added to the mixture to give the glass its purplish colour, suggesting that it had been designed to be decorative. Perhaps, Brill speculated, the slab had been destined to be broken up into small pieces and sent out to craftsmen in other villages, who would then have fashioned glass objects of their own from them. Or perhaps the intention had been to keep it in one piece and use it in a building as an impressive architectural feature. Robert Brill was doubtful that the answer would ever be forthcoming. He wrote:
We must in the meantime commend its unknown makers for their engineering skill. They brought over eleven tons of raw materials to a temperature in excess of 1000°C for several days, and produced a glassy consolidated mass. This was a considerable technological feat, and I know of no similar accomplishment in the metallurgical or other pyrotechnic arts in ancient times.
Dr Brill’s approach is realistic. There can be no definitive solutions to such mysteries, for, as far as we can tell, the ideas and technological secrets of so many ancient civilizations were not written down. The fact that the Californian Chinese anchors were thought mysterious shows how quickly know-how can be forgotten. Scientists can learn much about mysterious artefacts by experiment, the archaeologist’s spade can turn up many clues, but the exact intentions and methods of the people who traced out the huge pictures of the Nazca desert, of the Galilean glass-makers, the Inca builders and the metalworkers who worked a Chinese warlord’s belt are likely to stay lost forever in the tantalizing silence of the past.
Arthur C. Clarke comments:
I am happy to see a solution to the mystery of the ‘ancient’ Chinese aluminium belt, which has worried me for years. Technologically, such an artefact would be almost as anomalous as a medieval transistor radio. Of course, the solution may not be right, but it is highly plausible – and one possible solution is infinitely better than none. Recent scandals have shown that archaeological (and other scientific) frauds are by no means uncommon, and may begin as practical jokes that sometimes get out of hand. The classic case is that of the eighteenth-century German professor whose academic rivals carved amazing fake fossils for him to discover.