The concept of "ancient aliens" suggests that extraterrestrial beings visited Earth in ancient times and influenced human civilization. Proponents argue that certain historical structures, like the Pyramids of Giza and Stonehenge, exhibit advanced engineering techniques that they believe could not have been achieved by the technology of the time. Supporters of this theory often cite ancient texts and artifacts, such as the Sumerian tablets and Nazca Lines, as evidence of alien contact. They claim that these items depict advanced knowledge or technology that aligns with modern understandings of space and science, implying a connection between humans and extraterrestrial visitors.