Hi, what do you know about past civilizations on earth? About ancient countries like Egypt. One of the mysterious things in the world are pyramids. In the past they are made probably by slaves, they were as tomb. Well these are probable answers. But there are some theories about pyramids. As pyramids are made of huge stone which are not supposed to be possible to move and transport by human some theories say that aliens helped human for building these pyramids while there is no evidence for this theory. Let's watch the video to learn more about pyramids how it is built and its mystery.