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Inca Engineering

 

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Overview
About 90 years after Spaniards conquered the Inca Empire, Shakespeare wrote that "our life finds books in the running brooks and sermons in stones." Stone structures, road systems, agricultural terraces, and irrigation systems built in 1450 - 1540 A.D. by Incan engineers speak eloquently of a highly developed culture. Without machines, metal tools, or wheels, the Incas built structures that harmonize with natural outcroppings of stones found on the mountain tops. The precisely carved, carefully fitted stones required no mortar, yet have withstood 500 years of weather and earthquakes. The Incas used simple, labor-intensive technology to help carve and move the stones harvested from nearby rockfalls. Many weighed more than 100 metric tons. Stonemasons shaped the blocks using a simple, effective method called flaking and a neolithic tool called a hammer stone. Made of granite, quartzite, or olivine basalt, hammer stones have a hardness of at least 5.5 on the Mohs scale, about the same hardness as the larger stones. Striking at a 15- to 20-degree angle, stonemasons could chip off pieces of the rock; alterations in the angle and force of the blow determined the size of the chips. Twenty quarry workers took about two weeks to dress four sides of one stone measuring 4.5 by 3.2 by 1.7 meters (14.8 by 10.5 by 5.6 feet). Inclined planes, rope fashioned from the fourcroya andina plant, and gravity helped transportation crews move the stones. They moved the massive blocks across several kilometers of valley, through a shallow river, and up the mountain face to 2,400 meters (7,875 feet) above sea level, where their buildings still stand. In his account, Garcilaso de la Vega reported that "they moved them, dragging them with muscle power using thick ropes; nor were the roads along which they hauled them level, but very rough mountains with steep slopes over which they were moved up and down with sheer human strength." Excellent organization and management were required to accomplish this. Labor rather than money served to pay taxes, so a large labor force was seasonally available. Researchers estimate that 1,800 laborers were required to drag one 100-metric-ton block. This is equivalent to each laborer pulling approximately 54 kilograms (120 pounds). Evidence on or near the ramps suggests that the Incas may have used wet clay or gravel to reduce, which could have decreased the number of laborers needed to pull each stone. Incan engineers worked with their environment, economy, and people to fashion "sermons in stones" that have withstood centuries. Today's challenge is to withstand the thousands of visitors that come to marvel at their accomplishments.

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