Explorer Semir Osmanagic has recently returned from a visit to Mexico, in the town of Gudalahare, where he has been investigating the presence of stone balls, resembling those found across regions of Bosnia.

He found hundreds of stone balls on the Cerra Piedras Bollas hill. There was only one reference to these stone balls, reported in the National Geographic magazine in 1968. The archaologist who found and reported the stone balls could not believe that primitive Indian hands could have created the objects, which were up to 4m diametre and weighed as much as 50 tonnes.

He visited a geologist in the region who told him the local theory that the balls were thrown by a volcano, some 30km away, millions of years previously. However, most of these balls are concentrated on one hill in the region, so discounting that theory, in addition to the geometric shape of the balls.

Another local belief, that there was gold at the centre of the balls, has resulted in damage to many of the stone balls Osmanagic saw. All these balls must be the product of intelligent human beings, yet historians have all but ignored their presence – these objects have only, for example, received one small mention in National Geographic, several years before.

Little significance has been placed on their existence. On examining one of the balls in the village of Ahualulco del Mercado, Osmanavic concluded that it was created by the same methodology as that used to create stone balls in Costa Rica and Bosnia and using the same material. There is nothing in our current understanding of history that explains the presence of these stone balls.