How were these huge spheres made?
It is thought that the spheres first came from the bed of the Terraba river and were transported by natural processes; the granodiorite stone comes from the Talamanca mountains range, 50 miles away from their resting place. So far, unfinished spheres have not been found. A small number were made of coquina, a very hard material formed by the fusion of shells and sand that is found on beaches. It is not fully understood how these hard spheres were made, though the most likely method probably consisted of a combination of small fractures and grinding. Heat was possibly used as granodiorite exfoliates in layers when subjected to rapid temperature changes. It is possible that the spheres were thrown in fire and in cold water, while being hammered and pecked with tools made of the same material, and were finally polished to give them the small finish that amazes so many people. No metal tools were used.
What were the spheres used for?
It is believed that these balls were made by the ancestors of the indigenous people who live in the region, known today as the Borrucas, Teribe and Guaymi. They lived in dispersed settlements, of which the larger ones included around two thousand people. They grew beans, maize, manioc avocado, pineapple and medicinal plants.
To date, nobody has been able to give an explanation that could be proven as to the use of the spheres. Some believe that they were ceremonious stones used in burial sites, others believed they were arranged by people who knew about the use of astronomical alignments, or magnetic compasses, but as so many were moved from their original sites, nothing can really prove this theory. These spheres were found in some burial grounds with gold ornaments that date from AD 1000, however others were also found in strata that contains bits of Buenos Aires Polychrome that is a type of pottery of the Chiquiri Period of the year AD 800. Others have the pottery characteristics of the Aguas Buenas culture, whose dates range from around 200 BC to AD 800.