June 30, 2012

Ancient Egyptian Pyramids at Dahshur Part 3

The first explanation for the rhomboid shape was given early in the nineteenth century by Sir J. Gardner Wilkinson who suggested that the monument had to be completed in haste because the king died prematurely. Perring supported this view since he thought that the smaller packing blocks and less careful work in the upper part suggested a hurried construction. For two reasons this explanation is not convincing. In the first place, owing to the geometric shape of a pyramid, the quantity of stone that can be saved in changing the top part is not large. In the present case it amounts to only g per cent of the total masonry, an economy hardly worthwhile. Secondly, the next pyramid, the Red one, was entirely built at this lower angle.


Ancient Egyptian Pyramids
The second explanation given for the change in angle is that the superincumbent weight had to be reduced because cracks had developed in the building. It has also been argued that the cedar- wood beams in the upper chamber were introduced in order to shore up the structure against lateral pressure. Reasonable as this explanation might appear at first sight, the technological evidence is quite unconvincing. First of all, as was mentioned in the last chapter, the effect of pressure due to the weight of stone on the rest of the building is not serious and, moreover, the reduction in weight on lowering the angle of elevation amounts in this case to no more than 23 per cent. The cracks in the Bent Pyramid are small and could easily be plastered over. They are no worse than the cracks due to ‘settling’ in any other pyramid. As regards the cedar beams, they are at right angles to the acting force and, in any case, would have been easily broken by the forces involved. It is our opinion that they were not introduced later to save the structure, but that they were used as horizontal spacers while the pyramid was being built. They were not removed because, as the shape of the roof shows, the upper chamber was never finished. Far from being damaged, this corbelled roof presents the same aspect as the undressed roof slabs in the Meidum pyramid. There, incidentally, cedarwood spacers had been employed, too, and their remnants are still in situ. Altogether there existed in the Bent Pyramid itself no reason to reduce the superincumbent weight of masonry.

On the other hand, we have ample evidence that it was primarily the angle of elevation and not the weight which was considered perilous, and that the danger envisaged was not a crushing of the interior chambers but a slip of the outer mantle. It was this slip which had caused the disaster at Meidum and it appears an inescapable conclusion that the change in design of the Bent Pyramid was an effort to avoid a similar catastrophe at Dahshur. At the time when the Meidum pyramid collapsed, nothing could be altered at the half-finished Dahshur structure, except the construction of the packing and the outer casing. And for this there is, indeed, clear evidence. When the step pyramid at Meidum (E2) was transformed into a true pyramid (E3), packing blocks had been put onto the steps in horizontal layers. Moreover, these layers had been continued for about 6 m. beyond the outer limits of the supporting buttress walls. It was evidently here that the disaster occurred and the builders at Dahshur had to make sure that any repetition of it should be avoided. They were fully aware of Imhotep’s stabilising device of inwardly inclined buttress walls, composed of layers of masonry sloping towards the centre of the structure. In order to assure similar inward thrust by the outermost layers of the Bent Pyramid, they laid the packing blocks and also the casing stones not horizontally but in courses which slope inward at an angle of about 6°.

It is this apparently archaic feature in design, reminiscent of the structure of Zoser’s Step Pyramid, which induced the archaeologists for some time to date the Bent Pyramid before that of Meidum. From the evidence since discovered, revealing the name of Snofru in the Bent Pyramid and its valley building, we now know that it was the successor of the Meidum monument. The return of the builders to the earlier system of inward sloping courses was simply the result of their knowledge that this was a method ensuring increased stability. Moreover, the casing stones at the lower and steeper part of the Bent Pyramid are much larger than those employed at Meidum. Finally, whereas at Meidum the outer casing rested simply on sand, that of the Bent Pyramid is firmly supported by a limestone base which itself slopes inward. Thus everything was done to safeguard against plastic flow in the already existing part of the monument whose steep angle of elevation could not be lowered.

As for the upper part of the pyramid, the building-up of the core could now be done less steeply, at a gradient of 3/m instead of 4/m, which appreciably reduced the danger of slip for the packing blocks and casing. The somewhat laborious laying of inward sloping courses of masonry could here be dispensed with, nor was it necessary at this safe angle of elevation to employ large fitted casing stones. We therefore find, in the upper part again, horizontally laid packing blocks and small casing stones. These were the features which appeared to Perring and his successors as indications of less careful and hasty building. However, this impression is mainly caused by the selective activity of stone robbers who, after having scaled the lower part along the edges, found it much easier to remove casing stones resting on horizontal packing layers than at the steep lower section. There, the difficulty of dislodging large casing stones, lying at a camber, has saved larger areas of intact outer casing than at any other pyramid.

All these features the reduced angle of elevation, large blocks of inward sloping casing, and the firm foundation - render the Bent Pyramid a strongly confirmatory testimonial of the catastrophe which overtook the Meidum monument. These three structural changes turned the Bent Pyramid into a hybrid edifice which had been started as a steep true pyramid, outshining that at Meidum, but which then had to be converted midway in search of greater structural stability. It is interesting to follow the technological lessons which had been learnt at Meidum and were applied at Dahshur.

The wish to play safe, even at the cost of a less impressive appearance, completely dominated the design of the next monument : the Red Pyramid. Its height is similar to that of its southern predecessor which, however, it exceeds in volume, for the Red Pyramid was built throughout at the safe angle of elevation of 43|°. Owing to its good state of preservation and its great bulk, we know nothing about the underlying internal structure. It is, nevertheless, to be assumed that this too was constructed as a step pyramid on top of which was placed the marker needed to obtain the straight edges of the casing. While its main structure is well preserved, almost nothing is left of the casing. Owing to the gentle slope, this pyramid became an ideal quarry for stone robbers who were able to remove the blocks of dressed white limestone safely and without much difficulty. Today its appearance is characterised by the underlying packing blocks of reddish local stone which have given the building its name.

As in the upper part of the Bent Pyramid, the packing blocks of the Red Pyramid are laid in horizontal courses. These blocks are well-shaped, though not as carefully squared as those of the next pyramid at Giza. Altogether the two Dahshur pyramids show a transition from the small-scale masonry of the early step pyramids to the megalithic stonework at Giza. This distinction between the two different types of masonry was emphasised by Clarke and gngelbach in their standard work on ancient Egyptian masonry. As they point out, entirely new methods of handling had to be adopted as soon as the blocks employed became too heavy to be lifted by a few workmen; the use of lifting tackle was unknown in the pyramid age. These special skills had been needed in the Third Dynasty only sparingly, but we witness their employment on a very large scale at the Giza Pyramids.

Egyptian Pyramids at Dahshur :

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