The history of humanity spans several millennia, and historians will never know all of its secrets. Artefacts found during the course of archaeological excavation sometimes throw up questions which baffle even the most learned experts.
But this just makes the search for the truth even more interesting. We have compiled some rare facts and objects which are believed to be of aliens, which historians and archaeologists still can’t explain such as the giant stone spheres of Costa Rica. These mysterious stone formations are intriguing not only for their perfectly spherical shape but also on account of their unknown origins and purpose.