One of my reasons for thinking ET's have visited the planet are the Nazca Lines. They are only noticed via high altitude, much higher than the mountains and plains in the area.
The pyramids were built by humans, I don't believe aliens had any influence on that. With human hands, just about anything is possible, to the most minute detail. It just takes time. We must think back to how things were done hundreds and thousands of years ago. Machines didn't always exist to make our lives easier. LOL
The Nazca Lines are just a complete mystery to me, and the ET influence on their design and placement make sense. At least until I hear another theory on their existence. I love being open minded, I never completely dismiss a theory until I have hard evidence to prove one way or another.
Laters,
Brian