These are the world's most mysterious stone circles

Mysterious circles of megaliths (large monumental stones) have intrigued us for millennia. These enigmatic and often elaborate stoneworks are scattered around the British Isles, parts of Europe, Africa and the Middle East. Some were built for ceremonial reasons, others as ancient markers or astronomical instruments, and some for burials or social gatherings. But very often historians aren’t certain why these age-old structures were erected by our ancestors, which only adds to their mystique.