Some people propose that intelligent alien life came here (to earth) and oversaw the design and construction of great architectural works including the Great Pyramids of Egypt, Machu Picchu, and even some of the great Mayan temples.
Looking at the archaeological evidence, the history of architecture, anthropology, and countless other bodies of evidence, it is clear that all masonry structures on earth are man-made. This work was not done by aliens. To suggest that aliens are responsible for some of the best masonry construction diminishes some of humanity’s greatest accomplishments.
Is it possible that aliens could have visited earth and supervised construction? Sure, anything is possible: you just need proof, there is no proof. It is extremely improbable that aliens built the pyramids, or anything else. It is ridiculously improbable.
When the History Channel provides shows like Ancient Aliens, they do a disservice to early masons. It is something of a backhanded compliment to the incredible skill, knowledge, aesthetics and abilities of ancient masons: that these shows foolishly propose ancient aliens.
If you ponder the pyramids, or muse on Machu Picchu, or cherish Chichen Itza, then you are pondering the work of people. Not aliens.