Seen from above, the jagged rocks strewn about the Chincha Valley desert in Peru seem inconspicuous. But stand in the desert itself and these rocks form lines that stretch toward the horizon. Researchers have found that these lines were probably ancient signposts for the Paracas culture more than 2000 years ago, guiding people across the desert to gathering places for the winter solstice.

The Paracas people lived in what is now southern Peru from 800 to 100 B.C.E. They immediately preceded another culture called the Nazca, which is famous for making massive line drawings out of earth and stone, including enormous works of art depicting everything from birds to monkeys. Archaeologists call such lines “geoglyphs,” whether they are meant to be artistic or serve a practical purpose.

The Paracas also made geoglyphs, and the Chincha Valley contains two kinds, explains Charles Stanish, an archaeologist at the University of California, Los Angeles. By sweeping the darker desert soil off the bright limestone underneath, ancient peoples created white lines that are easily visible at great distances. “They would be unmistakable” to people traveling down to the desert from the surrounding hills, Stanish explains. Then, as these travelers arrived at certain spots on the desert floor, the second type of geoglyph would become obvious. What previously looked like nothing more than scattered rocks would suddenly take on a definite shape and appear to form new lines stretching off into the horizon.

To understand the purpose of the geoglyphs, Stanish and his team first had to confirm that the lines were made by the Paracas people. Scientists have a horribly difficult time pinning down when any geoglyphs were made because they include no remains from dead plants for carbon dating. However, the Chincha Valley also contains ruins of five settlements with small pyramids built by the Paracas that contain artifacts from daily life, such as pots and baskets. There are also three large mounds in the desert that contain the remains of maize and sugarcane that definitely came from 400 to 100 B.C.E., when the Paracas people dominated the region.

So the researchers played a 30-square-kilometer game of connect the dots. They used GPS technology to plot the desert’s settlements, mounds, and 71 geoglyphs for the first time. What they saw was unmistakable. Certain groups of geoglyphs clearly led directly to particular mounds or settlements, suggesting that they served as paths for Paracas people seeking to trade goods or gather for other activities, the researchers report online today in the Proceedings of the National Academy of Sciences.

Because each group of geoglyphs pointed the way to a different settlement, Stanish believes the settlements were likely controlled by distinct political or ethnic groups. Each group probably built its own set of geoglyphs in order to draw followers throughout the desert to its own trade fairs and other social events, he says. This discovery not only provides a glimpse of what life was like before the Nazca, he adds, but it also shows the roots of how society developed when the dominant culture had no real government. “They’re converting this landscape into a big theater, and the ultimate goal is to bring people together to market, exchange goods, manufacture goods, exchange marriage partners, gossip, do all the things people like doing. And then they’re competing with each other to bring in the most supporters,” Stanish says.

But that wasn’t all the researchers found. It appears that the three large mounds had a ceremonial purpose, because each was connected to separate pairs of geoglyphs that point directly to the spot where the sun sets on the winter solstice in June. There’s no evidence that people lived around the mounds, so Stanish suspects the Paracas used them as gathering places for yearly festivities tied specifically to the solstice. “When you stand behind the mounds and you’re facing the sunset—and we were there for the solstice—the sun sets right on the mound. And if you’re a human being standing there, the sun melts right on your head. It’s pretty impressive.”

The new research is “very sound,” says archaeoastronomer Anthony Aveni of Colgate University in Hamilton, New York, who was not involved in the study. He added that the findings hint at how astronomical awareness grew over the centuries in the region, beginning with recognition that the sun slowly travels back and forth, north and south, over the course of the year. “Here we have the more basic earlier observations being used, just simply following one of the extremes of the pendulumlike movement of the sun.”

Hendrik Van Gijseghem, a Nazca archaeologist at the University of Montreal in Canada, who was also not involved in the study, called the new work “tremendously interesting.” He says Stanish and his team’s effort to date the glyphs by connecting them with the Paracas mounds and settlements is convincing. “They can actually make a good case that there is a consistent association between well-dated settlements, these geoglyphs that are notoriously hard to date, and astronomical phenomenon.”

Now that the mounds’ ceremonial purpose is clear, the next step for Stanish’s team is to figure out the exact nature of the social events at the Paracas settlements. He plans to further excavate the settlements to look for objects such as beads, copper, shells, and the bones of llamas and alpacas. “There’s all sorts of things we can look for to see what kinds of activities were going on.”