What Are the Mysterious Stone Spheres of Costa Rica?

Deep in the Diquis Delta region of southwestern Costa Rica, fruit company bulldozers plowed down swathes of rainforest in the 1930s and dug drainage ditches to make way for banana plantations. In the process, they accidentally exposed a collection of remarkable objects: almost perfectly round spheres carved from hard volcanic rock. The largest one is massive, with a diameter of nearly nine feet and weighs 26 tons.

Research has since revealed the spheres were carved by Indigenous people who abandoned them and their communities before the 16th-century arrival of the Spaniards. Archaeologists have some understanding of their purpose—they believe the spheres were status symbols placed at the entryways of homes of important people. Research has also found that some spheres were aligned with astrological features, such as the location of the sunrise on the horizon at certain days of the year. 

Beyond that, any additional purposes, spiritual significance and the beliefs of the people who made them are educated guesswork. There has been speculation (dismissed by archaeologists) that they may have been markers for navigators from the mythical city of Atlantis, or even projectiles fired from alien ships to earth.

The train cars that shipped bananas from the plantations were then also used to send the objects known in Costa Rica as “Las Bolas de Piedra” (The Stone Balls) all over the country, says John Hoopes, a University of Kansas archaeology professor who specializes in southern Central America and northern South America and has researched the spheres in visits to Costa Rica since 1990. 

Some ended up as ornaments in front of Costa Rican office buildings and banks and three are on display in front of the Costa Rican congress building. Museums in New York and Denver have them and one is displayed on the campus of Harvard University.

The fact that so many were moved from their original locations has complicated research into the spheres’ purpose. Those that are still in the Diquis Delta and on a small island off the country’s Pacific coast were granted protection as national treasures in the 1980s and prohibited from being exported. Their locations were designated as World Heritage sites by UNESCO in 2014.

The Indigenous people who made the spheres lived on mounds with stone foundations to elevate their homes above the region’s frequent flooding. They used two different techniques to fashion sophisticated gold jewelry and made pottery featuring images of birds and crocodiles, Hoopes says.

They were members of societies ruled by chiefs in which “extensive farming and the availability of natural resources would have created favorable conditions to undertake important public infrastructure works, create monumental sculptures and obtain symbolic, deluxe goods according to their social condition,” according to the National Museum of Costa Rica.

Most spheres “were probably made by the Chiriqui culture (A.D. 800–1500), the last of three major pre-Colombian cultures in Costa Rica, during a period when villages began to form, with cobblestone house foundations, pavements, walls, and mounds,” Archaeology Magazine reports in an article citing museum archaeologist Francisco Corrales.

Hoopes says field work by Corrales in the 1990s found two stone spheres on both sides of the entrance ramp to a house platform, representing evidence that the spheres were status symbol ornaments.

It’s unclear whether the spheres had a spiritual or religious purpose. Some have theorized that the spheres might align with moon phases, suggesting a relationship with lunar cycles and the cosmos. Others have speculated that the spheres could represent eggs of sea turtles, which are spherical.

“Another possible explanation for the groupings of spheres is that they served as readings of constellations and/or as foundations for narrating creation myths or legends,” Corrales wrote in a 2021 research paper. Hoopes says his “own thinking is that these spheres represented human participation and control in the shaping of nature.”

The Indigenous people living in the Diquis Delta knew that it took time and energy for the rocks carried downstream from nearby volcanoes to be rounded and polished by strong river water forces, Hoopes says. “In making the spheres, they were taking that power for themselves and their shaping and rounding vested the object with power and energy,” he says. The spheres “became like magical objects.”

While the larger spheres get the most attention, some of those found are just three to eight inches in diameter. Small spheres were found at a Diquis Delta grave site by archaeologist Samuel Kirkland Lothrop, “who believed that small spheres could be considered personal property of sufficient importance to be carried to the afterlife,” Corrales wrote.

“He also surmised that small spheres could “stand-in” for—or, in some sense, represent—the larger ones, such that a small sphere in an alignment could have been a temporary substitute while a big one was being prepared for placement,” Corrales adds.

Spanish conquistadores started exploring the region in the 16th century, but didn’t report finding any spheres or indications of the civilization that made them.

Flooding covered the spheres with sediment, leaving some more than three feet underground in the rainforest and others embedded in the ground with their tops barely exposed.

What happened to the sphere-makers and why they disappeared is unknown. Catastrophic flooding in the region could have destroyed agricultural production for several seasons and prompted the abandonment of their communities, Hoopes says.

War might also have wiped them out or prompted them to move. That’s plausible, Hoopes says, because archaeologists have found stone statues in the region depicting people holding trophy heads, showing they were warlike and conducted decapitations.