According to his fellow researcher Dr. Sam Osmanagich, the region used to have many more of the spheres well into the 20th century. Many were apparently destroyed in the 1970s due to rumours there was gold hidden in the middle of them.

Dr Osmanagic, known as “the Bosnian Indiana Jones,” hit headlines in 2005 when he claimed that a cluster of hills in  Bosnia’s Visoko Valley was in fact the site of ancient pyramids linked by a network of underground tunnels.

While his claims were mocked by some, the Bosnian government gave financial backing enabling excavations to be carried out in the region. Nedzad Brankovic, Bosnian Prime Minister at the time: “We were told the world was laughing at us … but there is no government in the world that should stay quiet on things which are positive.”

Anthony Harding, the president of the European Association of Archaeologists, described the Visoko excavation as “a total absurdity”, saying: “There is some genuine archaeology on the hill and I’m told it’s medieval, possibly Bronze Age or Roman. But the speculation that there could be a 12,000-year-old structure beneath is a complete fantasy and anyone with basic knowledge of archaeology or history should recognise that.”

In 2016, critics are once again lining up to poke holes in Dr Osmanagic’s rather grand claims. Discussing the Zavidovici spehere, Mandy Edwards of the University of Manchester’s School of Earth, Atmospheric and Environmental Sciences told MailOnline the rock may not be man-made at all, and have been formed by the “precipitation of natural mineral cement within the spaces between sediment grains” – a process known as concretion.

Source: The Telegraph