Heavenly Valley

Question: What did the ancient Incas see reflected in the waters of the Urubamba River in Peru’s Sacred Valley?

Answer: The Milky Way

The Incas believed that the Urubamba River was the terrestrial reflection of the Milky Way and its constellations.

You know the Incas, of course. Revered for their advanced knowledge of astronomy, agriculture, and architecture, the Inca Empire flourished in the Andean region of South America from the early 15th century up until its conquest by the Spanish in the 1530s. And the Sacred Valley, a fertile land nestled between Cuzco and the lofty heights of Machu Picchu, was at its very heart.

Many people don’t realize just how big the Inca Empire was, however. Sprawling across the Pacific Coast and across the Andes to the edge of the Amazon, it took in parts of present-day Colombia, Ecuador, Peru, Bolivia, Chile, and Argentina, encompassing close to 800,000 square miles. At its height, the Inca people, who numbered only about 100,000, ruled over some 12 million people from close to 100 different ethnic groups, making it the largest empire of the ancient Americas—and one of the largest in the world at the time. Unfortunately, it was one of the shortest-lived ones as well.

So, with such a vast empire, why was it centered in the Sacred Valley—and what made this particular valley so sacred in the first place?

A river runs through it

When it came to the ideal locale for the headquarters of an expanding empire, the Sacred Valley checked all the boxes. First, the valley is set in a uniquely fertile geographic and climactic stretch of land high up in the Andes. The geography not only provided natural fortifications against invaders, but the high altitude itself made it more difficult for any invaders used to low altitudes. Plus, the varying altitudes of the valley created many different microclimates, which allowed for different types of crops to flourish—something the Inca took full advantage of while developing some of the most advanced agricultural techniques in the world. By blanketing the mountain slopes with terraces and sophisticated irrigation systems, the Incas were able to produce more than enough crops to sustain the resident population with staples including corn, potatoes, quinoa, fruits, and vegetables.

It was all made possible by the Urubamba River. The majestic waterway running the entire length of the Sacred Valley provided the Inca with their main source of water, made the soil fertile, and regulated the various microclimates. With its topography and the life-giving gift of the Urubamba River, the Incas regarded the Sacred Valley as the source of their strength and power, which was reflected in their belief system.

Inca religion grew out of the beliefs of other Andean people who have long worshipped the natural world around them, including mountains, rivers, lakes, the ocean—and constellations.

Keep your feet on the ground and keep reaching for the stars

Casey Kasem had the right idea about the Inca, who were always looking heavenward because they held celestial visions sacred. The stars and constellations of the Milky Way—and its earthly counterpart in the Urubamba River—twinkled and gleamed brilliantly for these ancient sky-watchers.

Without telescopes or written records, the Incas were able to map the night sky with astonishing accuracy. But the stars were more than distant lights to the Inca, they were divine entities. And their astronomical observations were used for everything from predicting weather and harvest times to scheduling sacred events. While several ancient civilizations observed the heavens, the Incas were unique in that they saw themselves as active participants in the heavens. Believing there was no separation between the earthly realm and the cosmos, the layout of many cities, temples, and monuments were built to align with celestial events.

The Incas had their own names for groupings of stars they observed like the Pleiades—the cluster we know as the “Seven Sisters,” for the number of stars a keen-eyed observer can count without a telescope. To Incan eyes, this stellar assemblage resembled a handful of seeds, so they called it the Collca, meaning storehouse.

At the latitude of the Sacred Valley, thirteen degrees south of the equator, the Collca/Pleiades cluster drops out of sight below the nighttime horizon every year in April. Then, it reappears in early June, shortly before the winter solstice. This timing, along with other celestial observations, helped Incan farmers to schedule their planting and harvesting, and the return of the Collca to visibility was marked with a sacred ceremony.

The Southern Cross, called Crux in modern astronomy, is another constellation that the Incas found useful. There is no Southern Hemisphere equivalent of the North Star, but the two stars on the long axis of the Southern Cross can be used to draw a line that points due south. In Machu Picchu, near the Intihuatana sun stone in the city’s Sacred District, there is another carved stone that shows the Incas knew this fact well. Its diamond (or kite-like) shape mimics the outline of the Southern Cross, and it is precisely oriented on a north-south axis matching that of the constellation.

The Incas regarded the Milky Way, which they called Mayu, as a celestial river. For part of each year, Mayu’s orientation in the sky parallels the course of the Urubamba River (which they called the Vilcanota) through the Sacred Valley, contributing to the Incan view of objects in the night sky as sacred reflections of their counterparts on the ground.

Another unique feature of Incan astronomy—found in no other culture on Earth—was the recognition of dark constellations in the shadowy parts of the Milky Way. Today, we know these dark areas are caused by non-luminous clouds of dust and gas that obscure the stars beyond them. The Incas saw shapes in these shadows that represented more connections between earth and sky, including Hamp’atu (the Toad), Atoq (the Fox), Yutu (the Tinamou, a partridge-like bird), and Machacuay (the Serpent, viewed positively by the Incas as the god of all things beneath the earth).

Three of the most prominent dark constellations further demonstrate the links the Incas made between worlds above and below. The largest of these shadow-shapes is the Llama, with the Baby Llama underneath it and the Shepherd standing watch next to them. The large Llama is the only one of the dark constellations to also include stars, with the bright beacons known today as Alpha and Beta Centauri representing its eyes. In the dark skies of centuries ago, all of these sights must have been awe-inspiring nightly reminders of the Incan worldview. Today, we can still see how these ancient people bound heaven and earth together by putting the Southern Cross on the ground and placing the llamas with their shepherd in the sky.

A good look at the night sky anywhere offers a mind-expanding vista of other worlds. But in the Andean realm of the Incas, it also yields a look deep into the spirit of their culture—whose propensity for stargazing still resonates with anyone who has ever looked upward on a clear night and contemplated our connections to the cosmos.

The Inca's profound connection with nature and the cosmos is evident in the numerous archaeological sites that dot the Sacred Valley—each with a story to tell of a civilization that lived in harmony with nature and the heavens.

10 fascinating facts about Machu Picchu & the Sacred Valley:

• Leave the kilt at home—The official rules of entry for Machu Picchu stipulate that it is illegal to enter the ruins wearing another country’s national dress.


• Tater lots—While "only" about 300 varieties of potatoes survive in Peru, prior to the Spanish invasion several thousand types of potatoes were grown in the fertile soil of the Sacred Valley.


• Corn flukes—A mild and delicious type of corn called "giant white corn from Cuzco" is still grown in the Sacred Valley and shipped around the world. It has the largest kernels in the world.


• Like a rolling stone—Like all Inca cities, Machu Picchu was purpose-built to withstand earthquakes through the use of ashlar masonry. This entailed cutting massive stones so precisely that they fit together without mortar, which allowed the walls to move slightly and then settle back in place should a seismic event occur.


• Flood control—Ashlar masonry, combined with terraces and drainage systems to prevent landslides and floods, is why Inca cities have lasted for centuries. And they built their cities and vast empire without the use of modern tools, ironworks, currency, powerful draft animals—or even the wheel, which the Incas hadn’t yet discovered.


• Watch out for the speed traps— To support the vast empire at its peak, the Incas developed a system of roads that stretched for almost 25,000 miles—about three times the diameter of the Earth.


• Even the Spanish were impressed—As the Spanish rapidly conquered the Inca Empire, they noticed how the cities they were plundering of their gold and silver were just as large as those in Europe—but cleaner and more orderly. And there is no question that the road and aqueduct systems of the Inca were superior to those in Europe at the time.


• No letters home to mom—While having no written language, the Incas used quipus, an elaborate data system of colored strings with knots to record information and keep track of their vast empire.


• Runners with altitude—To maintain communication across their empire, the Incas used a network of fleet-footed runners, called chasquis, who could cover up to 150 miles in a day.


• Germ warfare—With the better weapons of the Spanish, the Inca Empire was probably doomed from the start. But it wasn’t guns and cannons that destroyed the Inca civilization. The most powerful weapons the Spanish brought with them from across the seas were the diseases that the Incas had never been exposed to. Smallpox wiped out much of the Inca population.

Explore the Sacred Valley of the Incas and visit Machu Picchu during O.A.T.’s Machu Picchu & the Galápagos adventure.