According to Brien Foerster, the pyramids and other Megalithic architecture may have been the product of another race of aliens, who possessed ancient lost technology. If you examine for example Peru, where in Cusco there is Megalithic next to Inca architecture, you can see clearly that the earlier construction was not done with bronze tools, but very precise machines. In fact some of the basalt mega-ton stones may have been melted which would have required temperatures of 2000 degrees Celsius. https://www.youtube.com/results?search_query=brien+foerster