Costa Rica’s stone spheres were carved almost perfectly round, and no one knows why

Buried for centuries beneath the jungle floor of southern Costa Rica, and later uncovered by bulldozers clearing land for banana plantations, more than 300 carved stone balls sit scattered across the Diquís Delta and a small offshore island. Some are barely larger than a bowling ball, while others stretch more than two meters across and weigh as much as 15 tons. Archaeologists broadly agree that a culture long since vanished from the region carved them by hand centuries before European contact. What that culture meant them to represent has never been settled.

Hundreds of Spheres Tied to a Vanished Culture

The spheres, known locally as bolas de piedra, are attributed to the Diquís culture, which occupied the delta of the Térraba River from roughly 500 to 1500 CE. They rank among the best-known stone sculptures produced anywhere in the broader Isthmo-Colombian region that stretches from lower Central America into northern South America. Sizes range from a few centimeters across to more than two meters in diameter, and the largest examples weigh as much as 15 tons, heavy enough that moving even a finished sphere a short distance would have required a coordinated team of laborers.

Shaped by Hammer and Sand, Not Machinery

Most spheres were carved from gabbro, a coarse-grained volcanic rock similar in composition to basalt, quarried from hillsides several kilometers from where the finished pieces now rest; a handful of unfinished examples still sit in those original quarry areas. A smaller number were shaped instead from shell-rich limestone or sandstone. The carving method itself looks to have been direct and laborious rather than technically exotic: workers hammered natural boulders into rough spherical shapes using other stones, then smoothed the surface by polishing it with sand. The degree of finishing varies considerably from one sphere to the next, suggesting either different skill levels among the carvers or spheres meant for different purposes or status levels.

Lined Up Outside a Chief’s House

The clearest archaeological pattern is positional: spheres appear to have been arranged in straight lines along the approach to the residences of local chiefs, based on excavations at sites including Finca 6 in the Diquís Delta. What the arrangement was meant to communicate, whether status, cosmology, or something else entirely, remains an open question. One hypothesis holds that the spheres symbolized celestial bodies, representing the sun and moon at different points in their visible cycles, including full and half phases and the moments of rising and setting. Dating tied to the Aguas Buenas period, roughly 300 to 800 CE, and the later Chiriquí period, roughly 800 to 1550 CE, suggests the practice of carving spheres began around 600 CE and continued past 1000 CE, ending sometime before the Spanish conquest of the region.

Bulldozers, Dynamite, and a Hunt for Gold

The spheres came to wider attention only in the 1930s, when the United Fruit Company cleared dense jungle in the area to plant bananas. Heavy equipment operators pushed spheres out of the way with bulldozers, damaging a number of them in the process, and rumors of hidden treasure led some workmen to drill holes into the stones and blow them open with dynamite in search of gold that was never there. Several spheres were destroyed before local authorities stepped in to stop the practice. Some of the dynamited pieces have since been reassembled and put on display at the National Museum of Costa Rica in San José, which holds six spheres in its permanent collection, while many others ended up scattered across the country as lawn decorations.

How Round Are They, Really?

Popular accounts often describe the spheres as mathematically perfect, but the archaeological record complicates that claim. Some measured examples vary by more than five centimeters in diameter, and centuries of weathering and physical damage make it impossible to know their exact original dimensions. A review of the measurement methods used by early researcher Samuel Kirkland Lothrop found that his published diameters, listed to three decimal places, were actually averages calculated from tape measurements nowhere near that precise, a detail later writers overlooked when citing his figures as proof of extraordinary accuracy. That gap between reputation and evidence has not stopped speculative theories from spreading, including claims that the spheres originated in Atlantis or that a plant-based potion was used to soften the rock before shaping it, an idea undercut by the fact that gabbro strongly resists the kind of acidic solutions such a potion would require.

A National Symbol With Ongoing Research

The first scientific investigation of the spheres was carried out by Doris Stone, the daughter of a United Fruit Company executive, who published her findings in 1943. Her work drew the attention of Harvard’s Peabody Museum, whose researcher Samuel Kirkland Lothrop later published a more extensive study, Archaeology of the Diquís Delta, Costa Rica, in 1963. A 2010 site evaluation by University of Kansas researcher John Hoopes helped support a successful nomination, and in June 2014 UNESCO added four related sites, Finca 6, Batambal, El Silencio, and Grijalba-2, to its World Heritage list under the name Precolumbian Chiefdom Settlements with Stone Spheres of the Diquís. The same year, Costa Rica formally declared the spheres a national symbol, and examples now stand on public display outside the country’s Legislative Assembly and Supreme Court buildings in San José. Additional detail on the spheres’ dating and discovery is available through Wikipedia’s entry on the stone spheres.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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