Who do you think built it?
Idk but at many of these ancient sites they fail to unearth any building implements. Strange they never mention what they actually do find other than the stone structures. You'd expect if they found anything like pottery or any evidence of civilization other than the structures themselves, they would put forth those findings. They just always say they never find any stone cutting tools but mention nothing else. What else did they find? What didn't they find? Were the stone structures the ONLY things unearthed? They just focus on the structures and that there were no stone cutting tools found. Makes you wonder why they only focus on those two things.
One of my favorite episodes of ancient aliens is here:
This episode is called Aliens & Ancient Engineers. If you get a chance check it out.