The fortress-temple of Ollantaytambo is famous for its beautifully fitted great slabs of red porphyry forming a portion of what must have been intended to be its principal temple. But this complex, a work in progress when the conquistadores arrived, was never finished. A number of large cut blocks were abandoned en route to the site and remain today, known as piedras cansadas or "tired stones". Within the complex, a stone that was in the process of being maneuvered into its final position can be seen lying on its emplacement ramp. Other stones exhibit peculiar grooves which were meant to be filled with molten bronze or copper to lock two adjacent stones together (as was done by the Greeks in their temple construction, and also by the people of Tiwanaku near Lake Titikaka).
How the Inka cut stone without iron tools is not known with any certainty, but in all likelihood stone was cut and shaped mainly with stone tools. Bronze or copper tools may also have been used, but would be of limited use with the hard varieties of igneous rock commonly used by the Inka. In Cusco can be seen an interesting stone that was evidently abandoned while being cut in two; the row of narrow holes forming the line along which it was to be split seem to bespeak the use of a metal tool. Probably this stone represents post-conquest work for the Spaniards. The conquistadores admired Inka stonework sufficiently to employ Inka stonecutters and techniques in colonial buildings, and many of the "ancient Inka" walls in Cusco belong to the colonial period, such as this wall with carved snakes and stones in non-Incaic shapes.
Scribing and coping:
In 1987, architect Vincent R. Lee proposed that the Inkas used a technique known as scribing and coping to fit their wonderful jigsaw-puzzle stones. This technique is used to shape dove-tail joins of logs at the corners of log cabins, resulting in logs carefully fitted together with little or no gap between the cut log faces. A related technique could have been used by the Inkas to shape their stones.
If the Inkas employed the scribing and coping method, the process might have been something like this. To keep the illustration simple, we'll start with a simple rectangular wall block that is to be set in a notch or seat carved in the underlying wall stones or bedrock. A good example of rectangular blocks set in bedrock notches can be seen in this foundation wall at Pisac. Our rectangular block has a bottom, top, and two ends that must be fitted to their bedrock seat and the neighboring stones in the wall. The front and back sides do not have to be shaped for any particular fit. First the bottom and two ends are cut to a rectangular shape. Next the seat and faces in the underlying stones must be cut to fit this block. To do this, the block must be suspended above the stone on which it is to be seated. For very heavy stones, this is not a trivial problem, but perhaps the stone could be propped up by logs leaning in diagonally from the front and back sides. Now, the cut outline of the suspended block is traced with a scribing device
That the scribing and coping technique is a practical solution to the mystery of the Inka stoneshaping methods was demonstrated by modern stonecutters under the direction of Vincent Lee in the 1995 NOVA program "Inca". Whether or not it was the technique used by the Inka may never be known, but no other practical solution to the problem has been discovered.
closely fitted only to depths of a few centimeters from the outer face, with any leftover space between the rest of the vertical joins being filled with sediment.
Inka walls:
What the Inkas must have considered their very finest stonework is found, naturally, in their most important buildings, their temples. Temple walls are battered (inwards sloping), and constructed of finely hewn ashlars laid in courses that get progressively thinner upwards. This creates a wall with a wonderfully stable and pleasing appearance, and which is, in fact, highly resistant to seismic shaking. Earthquakes are a common building hazard in the Andean region, and Inka stonework has survived for centuries, even as Spanish colonial structures have collapsed. In fact, the most durable Spanish constructions have been those that incorporated Inka walls. Here original Inka walls have been breached by Spanish colonial doorways; note the inward slope of the lower wall, as opposed to the vertical upper wall of European construction.
The inside face of these sloping walls is normally plumb, as seen here in the fine stonework inside the Coricancha, the Inka "holy of holies" in Cusco. Thus the walls were thicker at the base, where the more massive courses were laid, and somewhat thinner higher up where the courses were smaller..
Of course, not all Inka buildings were built of fine stonework. Buildings of lesser importance might be constructed of rough stones set in mud, in a style known as pirca.
