I'm not sure about the idea espoused by another commenter that Europeans are descended entirely from Visigoths and Vandals and therefore Europeans were backwards. Angkor Wat is from the 1120s, Tenochtitlan is generally dated from 1325, Machu Picchu is around the 1420s, Oxford University by comparison dates from 1096, around the same time as the Tower of London - I don't know why anyone would presume any of these places are built by aliens - they're relatively young by historical standards.

Except the Egyptian Pyramids - aliens definitely did those. I've seen Stargate, I know the esoteric secrets.