The Incas displayed an enormous amount of energy in building temples, palaces, administration centers and road systems across their vast territory, during their 100 years of dominance in the Andes. According to Federico Kauffman D, such cyclopean task was motivated by politics and social control issues. A developing state required a large amount of administrative and religious staff, and it had to dazzle groups conquered with construction work, while always moving, and keeping a strong army and bureaucracy.
In this manner, the Inca architecture we admire these days had a religious and administrative purpose, rather than an urban one, as the sites of Vilcashuaman, Tambo Colorado, Huanuco Pampa, and Machu Picchu itself, demonstrate. Yet, this model didn´t belong solely to the Incas. At this moment it is important to remember that Peruvian monumental architecture started more than four thousand years ago, during the initial period, with Caral, Las Aldas and then Chavin. If truth be told, those who built them had little to envy from their peers in Cusco. For example, in sites such as Chan Chan and the Huacas in Moche, great ceremonial spaces were built surrounded by modest and even precarious urban areas.
Still, the Incas learned many of these techniques; the majority inherited from the Tiahuanaco-Huari period, and took them to a whole new level. Following a hierarchy, constructions used for urban, or agricultural and cattle-breeding purposes where built with unpolished boulders and fitted one to the other with small rocks. This type of wall is called pirca or perqa.
On the other hand, state and religious constructions were built with carved rocks, some of great dimensions, and others fitted like a puzzle using medium-sized materials. The rocks they chose were mainly hard such as granite, diorite and porphyry, and were mostly extracted from nearby quarries and transported to the construction site to be carved onsite.
It is believed that the large blocks of rock were transported through humid, muddy roads, to reduce friction. Even so, it is almost impossible to imagine the large amount of man force needed to move the gigantic blocks that gave life to Sacsayhuaman or Machu Picchu. Perhaps they were transported by mitimaes (displaced laborers) brought from villages conquered in faraway lands, or by groups of laborers just fulfilling their tasks, or collaborating voluntarily.
Inca architects would choose which type of rock to use according to the function the building would fulfill: for administrative buildings and noble houses, medium rocks, and for fortresses and religious sites, enormous ones. In both cases the rocks were carved completely and not only on their outer edge, to ensure that the joints were perfect, and that not even a pin could go through them. This also ensured that the construction would last in time. What's more, if we consider that this solidity was accompanied by an efficient drainage system, and by solid foundations, it is possible to say that Inca walls are eternal.
However, what is really impressive is that the Incas were able to trace complex terrace systems, cities perched on mountains, and buildings with foundations that have survived strong earthquakes, without any writing or plans. In fact, we still don´t know much about the tools they used to break and carve rocks, or to transport the massive blocks used in some walls. Regarding this last topic, Betanzos, a chronicler, states that they would use inclined areas of land covered with fine humid clay as ramps.
As for the type of slabs used, Kauffman asserts that there is no chronological difference between them, but that they were employed differently. So, while regular blocks were used to build perfect walls like the ones found in the Temple of the Sun in Machu Picchu, in others, regular blocks were lowered in their joints until forming “rounded” walls. One type of block they used is the so-called polygonal, such as the one found in Hatun Rumiyoc street in Cusco, in which the rocks fit perfectly like in a puzzle, or the walls that combine rock on the base, and adobe on the upper part like in the temple of Raqchi.