A field of perfect spheres
In the Diquís Delta of southern Costa Rica, more than 300 stone spheres are found there. Known locally as Las Bolas, these objects are remarkable for their near-perfect sphericity. They range in size from a few centimeters in diameter to over 2.6 meters, with the largest weighing an estimated 24 tons. The people of the Diquís culture, who flourished from around 700 to 1530 CE, crafted these monuments without metal tools. The primary material is gabbro, a coarse-grained igneous rock similar to basalt, which artisans likely sourced from quarries several kilometers away. A smaller number of spheres are made from limestone or sandstone.
The production method involved shaping boulders by hammering them with denser rocks, a process called pecking. They then ground the surface, possibly using sand as an abrasive, to achieve a smooth finish. While most of the spheres are unadorned, some feature carved petroglyphs, though weathering often makes them difficult to see. These massive, precisely shaped stones were first brought to widespread attention in the 1930s when the United Fruit Company began clearing jungle for banana plantations. Unfortunately, beliefs that the spheres contained gold led to many being damaged by dynamite.
Alignments and meaning
The original placement of the spheres appears deliberate. At archaeological sites like Finca 6—a UNESCO World Heritage site—some spheres remain in their original arrangements. Researchers have documented spheres arranged in straight lines, arcs, and triangles. Some of these alignments correspond with astronomical events. Lines of spheres have been found to point toward magnetic north or to mark the solstices and equinoxes, suggesting their use as a form of astronomical calendar to track seasons for agriculture or ceremony. One set of spheres at Finca 6 aligns with the sun on the subsolar point, which occurs twice a year in the tropics when the sun is directly overhead and objects cast no shadow.
The precise meaning of the spheres is not fully understood, as the Diquís culture disappeared after the Spanish conquest and left no written records. Beyond their astronomical function, theories suggest they served as markers of status and power, often placed at the entrances to the dwellings of chiefs or in public plazas. Their sheer size and the labor required to create and move them would have been a display of a leader's resources. The near-perfect circular shape may also represent a cosmological order, with the spheres acting as symbols of celestial bodies like the sun and moon.