In the 13th century, a small group of people living high in the Andes Mountains migrated down into the valley of Cuzco in southeastern Peru. Just over 200 years later, that initial band of travelers had grown into a mighty empire covering most of the Andes with an estimated population of nine to 16 million people. That empire belonged to the Incas, and although it thrived only from 1438 until the Spanish conquered it in 1532, its accomplishments were remarkable. The Incas gave birth to ideas and inventions still in use today.
The might and reach of the Incan empire is all the more impressive because it developed without currency, the wheel or a written form of communication.
What it did have, however, was a highly developed organizational system and a near limitless workforce that helped create a culture in which wonders -- such as the hauntingly beautiful Machu Picchu complex -- abounded. Here are five of them.
The Incas, of course, didn't invent the road -- that honor would no doubt go to the Romans -- but they did invent a network of roads and highways that connected their territory on a scale never seen before in South America.
At its peak, the Incan highway system covered nearly 25,000 miles (40,000 kilometers) with roads that ranged from 3 to 13 feet (1 to 4 meters) in width and consisted of everything from simple dirt paths to passageways covered in fine paving stones [source: McEwan]. The network had main thoroughfares known as the imperial highway system, or Capac-Nan. These roads ran on a more or less north-south trajectory, with one hugging the coastline and another running roughly parallel through the mountains. Smaller roads connected the two main arteries with all of the provincial centers of the empire. The entire system was reserved for government officials; if you were a commoner, you needed to seek special permission to walk the Capac-Nan.
Official business parties could travel approximately 20 miles (32 kilometers) per day along the Capac-Nan [source: McEwan]. Resting stations known as tampus were located along the roadways at approximately the same distance to offer travelers food, lodging and a chance to resupply. Rest was critical for these groups -- especially for the men whose shoulders carried nobles on raised platforms known as litters.
In the rugged, gorge-filled terrain of the Andes Mountains, there are places where roads alone would fail to provide adequate transportation. But, as was the case with most obstacles they encountered, the Incas had a solution: bridges.
Unlike the arched stone bridges built in Europe at the time, the Incas used rope to construct suspension bridges across mountain chasms, as they had long been experts at weaving materials from natural fibers. Since there were no wheeled vehicles, the rope bridges worked beautifully for foot traffic, conveying both man and beast with ease.
During bridge construction, large rope cables were formed from smaller ropes woven from llama and alpaca wool, as well as from grass and cotton. These were attached to stone structures on either side of the crossing. More of the thick cables were stretched to form handrails as well as the floor of the bridge, which was then covered with wood and sticks.
Longer than any stone bridge in Europe at the time, the Incan bridges spanned openings of at least 150 feet (46 meters). Travelers often crossed in the morning, as strong winds later in the day could cause the bridges to swing wildly like hammocks.
Because the materials that created the bridges were organic and biodegradable, they had to be rebuilt every year. Often, communities living near the bridges carried out this function.
In addition to verbal messages conveyed by runners, information was relayed across the roads and bridges of the Incan empire through the passing of items known as khipus (sometimes spelled "quipus").
These communication devices consisted of a main cord (the primary cord) from which a series of knotted strings of varying length and color were suspended (pendant cords). The strings were woven from cotton or the wool from llamas or alpacas. It's believed that the number of knots -- as well as knot types and their position on each pendant cord -- was used for record keeping according to a decimal system. The cords were likely used to keep stock of various commodities stored in qolqas, or warehouses, that were located across the empire.
To this day, unlocking the messages contained in the khipus has been impossible, but researchers at Harvard University have begun the Khipu Database Project. Started in 2002, the project is attempting to centralize all known information about khipus and feed it into a database that will compare and contrast various patterns of khipu construction. The hope is to develop a Rosetta stone of sorts that will untangle the ancient messages hidden in the strings.
Living among the steep peaks of the Andes, the Incas lacked level fields for farming. To solve this problem, they developed a system of terraces that they constructed throughout the empire like giant green staircases.
Building stepped terraces help the Incas create farmland, and the clever construction of each terrace gave crops the best chance of survival. The first step in construction was building stone retaining walls. These absorbed heat from the sun during the day and radiated it back out at night, often keeping crops from freezing in the chilling nighttime temperatures. Each terrace was filled with a base layer of medium-sized gravel, which was then topped with a mixture of fine sand and more gravel. On top of this, farmers placed a layer of topsoil into which the seeds of their primary crops -- corn and potatoes were top choices -- would be sown.
Occasionally, the terraces would fail to be productive. If this happened, the Incas would turn to a planting method known as "the three sisters." First, they would plant corn. Then, when the corn reached an adequate height, beans would go in the ground and grow up the stalks of the corn. Finally, they'd plant squash in the remaining spaces. This not only produced three crops from one terrace, but the beans fixed nitrogen -- making it available as a nutrient in the soil -- for the corn. The squash acted as mulch for the soil, keeping it moist and relatively weed free.
In the highest altitudes of the Andes, freezing temperatures are pretty much guaranteed at night. The Incas used this to their advantage by bringing potatoes to these chilly environments and letting them freeze beneath a cloth. The residents of the wintry villages would then walk on the cloths in the morning to squeeze out the moisture from the potatoes. The repeated process would result in freeze-dried potatoes known as chuño.
This product had several distinct advantages in the Incan empire, as it does today. First, it was lightweight. This allowed soldiers to carry large quantities of it with them on their campaigns with relatively little effort. Second, chuño, like all freeze-dried food, is extremely durable and can keep for years without being refrigerated. This made an excellent backup food source in case of drought, natural disaster or any other type of crop failure. Even today, in the case of crop failure, Andean highland natives will rely upon chuño to get through the difficult times. Lastly, the freeze-drying process would eliminate the bitter taste from some species of potatoes, making them much more palatable.
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