More than a thousand huge stone balls are scattered in the delta of the Diquis River in Costa Rica. The bolas grandes, as the locals say, are four meters in diameter and weigh more than twenty tons. Most of them are made of granodiorite, a very hard rock like granite, while the rest are made of coquina, a hard calcareous material. Since none of the two materials is found in that location, scientists believe that the balls were probably moved there after being created.
As for how they could be constructed, one theory says that the manufacturers gave the final shape carving them with knives, while another theory is based on the fact that the rocks tend to get curved forms if pieces of rock heated by fire and then poured in cold water. However, regardless of the technique, the obvious question arises: why so much trouble for these balls? What do they symbolize? Until now, scientists have not given a clear answer.