Made up of more than 10,000,000 people across 770,000 square miles, the Incan (also Inca or Inka) Empire of pre-Columbian America was notable for its long-lasting cultural impact on South American civilization, along with a host of innovations across agriculture, architecture and record-keeping.

However, like other empires quick to expand across conquered territory, the Inca faced a challenge: ensuring the safe movement of people and goods within its borders. Their solution? The Inca road system or “Qhapaq Ñan” — a network of interconnected highways and bridges that spanned nearly 25,000 miles and made its way through everything from humid jungles to snowy mountain peaks and arid deserts. Even more impressive? This Andean road system was built without the aid of wheeled carts or iron tools, and yet much of it remains to this day.

So, let’s explore this ancient road system with a look at its role in Incan operations, the effort undertaken to build and maintain this navigation network, how Incan engineers overcome critical landscape challenges and how this pre-Columbian construction marvel continues to impact South American culture.

Qhapaq Ñan: The Arteries of an Empire

While “all roads lead to Rome” is a European conceit, the Inca Empire had their own version: All roads of the Qhapaq Ñan lead to the capital of Cuzco.

From the city, four main highways branched out: Chinchaysuyu (north), Collasuyu (south), Antisuyu (east), and Cuntisuyu (west). Each led to a quarter of the Empire. The structure makes sense; not only does it conform to the four cardinal compass directions, but it also lines up with the Incan name for their empire, Tawantinsuyo, which means “Land of the Four Quarters” or “The Four Parts Together.”

With ten million people speaking at least 30 different languages — but just 40,000 Incas in charge of running the empire — this road system wasn’t just for show. While part of the project stemmed from the need for physical reminders of Incan leadership in conquered territories, the road’s primary purpose was much more practical: empowering easy movement. In effect, these Inca roads were the arteries of the empire, allowing its lifeblood — people and goods — to travel quickly and safely from place to place. Without the Herculean effort undertaken by Inca builders, even the best-laid administrative plans would quickly come to naught; reliable roadways showcased both strength and sustainability.

But this raises a question: How did Incan engineers manage to construct this continent-spanning marvel without the aid of iron tools, pack animals or carts?

Building the Inca Road System

The Qhapaq Ñan is now a UNESCO World Heritage site, and deservedly so. Also called the “Royal Road” or “Main Andean Road,” it not only included four main highways but also multiple smaller routes connecting cities and towns all along the west coast of South America. While some of the highways used preexisting routes built by other cultures in the area, Inca Empire engineers weren’t afraid to embrace the landscape and take on the challenge of creating new routes that snake through mountain passes or across blazing-hot deserts.

According to the Ancient History Encyclopedia, the Incans had only wooden, stone and bronze tools and lacked the advantages of modern surveying equipment to mark distances or account for variances in local terrain. While most road surfaces were constructed using packed sand, earth or grass, they varied in width from three to twelve feet — and some main highways were over 40 feet wide. In many cases, builders used small stone walls to mark road edges, while regular drains and culverts were used to divert water off or under main routes. As the journal Archaeologies reports, this roadway system also included structures placed at regular intervals called “tampus,” which served as lodging facilities for travelers and included space to store goods or materials being transported. In addition, major highways often included stone markers to indicate distance traveled in “topo,” an Incan unit of distance equal to seven kilometers.

It’s also worth noting that Incan roadway construction varied significantly by territory, since it was the responsibility of local populations to both build and maintain these roads. As the National Museum of the American Indian explains, using a give-and-take concept known as Mit’a and Anyi — or labor and reciprocity — the head of each household was required to pay a labor tax (Mit’a) by working on agricultural, military or construction projects for a specific amount of time each year. In return (Anyi), the Incan government provided food and security.

The (Not So) Straight and Narrow

Perhaps one of the most incredible aspects of the Qhapaq Ñan was the willingness of Inca builders to both work with natural landscapes and conquer any challenges they presented. For example, while Incan engineers have often been praised for their ability to create uniform roadways with ancient tools, all but the most well-traveled highways tend to follow naturally-existing pathways rather than fighting these contours. The Incan exception came when they encountered steep ravines or rushing rivers; rather than trying to find a way around or head downstream to discover a shallow ford, engineers tackled the problem head-on by building either rope suspension bridges or “oroya,” suspended baskets that could transport a few passengers at once over far greater distances.

Consider the suspension bridge over the Apurimac River, which measured 45 meters in length. Local populations were responsible for gathering, soaking, pounding and drying bushels of long grass that they then wove into strong fibers, stretched across the river, and lashed to rocky outcroppings. And with substantial degradation from repeated use, many communities had to complete the same process year after year to ensure bridges were safely maintained for all travelers.

Acknowledging the Qhapaq Ñan Legacy

Today, many paths on the Inca road system remain in use. Perhaps the most famous are the stairways and bridges surrounding popular tourist destinations such as Machu Picchu, but many modern roads use these pre-Columbian roadways as inspiration for current routes. As Smithsonian Magazine notes, technical traditions around Qhapaq Ñan construction remain. Every year, four villages in the Andes undertake a three-day festival to create a new rope suspension bridge, cut the old one free into the river below and replace it with the fruits of their substantive labors. Using virtually the same techniques as their Incan ancestors, young men haul massive fiber ropes into yawning chasm while village elders say prayers and make offerings. When construction is complete, leaders from each side of the river meet in the middle of their newly-minted effort and declare “Tukuushis” — we’ve finished.

This is the legacy of the Main Andean Road. While construction began more than six hundred years ago and the empire’s use declined rapidly after the arrival of Europeans, the effort and engineering skill required to create this roadway system — all without the convenience of modern tools or even iron implements — cements its status as both an ancient architectural marvel and enduring human achievement.