Travel: Teotihuacan in Mexico

My love of Indiana Jones notwithstanding, I have never been a big believer of aliens.  I know that the universe is a big place and surely there must be something out there other than ourselves.  Fine, amoeba perhaps, but surely not some creatures with spaceships that might have dropped by for a visit at some point.  After my trip to Teotihuacan, I am thinking that the Indiana Jones, Kingdom of the Crystal Skull premise might not be so far fetched after all? I mean, I do not understand how these pyramids were built.   They were apparently built between 100BC and 250 AD.  The American continent did not have any beast of burden at the time.  So no cows, or oxen or horses which were all brought by the Spanish over 1000 years later.  There were some llamas and alpacas in Peru but not in North America.   They also did not have the wheel (how they had not figured out the wheel is a mystery as well - I mean stones roll, logs roll, skulls roll).  The stone required to build these structures would have had to be hand carried one by one from somewhere over 50 km away.  So no wheel, no animals, but they did have a kind of concrete they used to keep the structures in place?  Ok maybe aliens is a bit far fetched.  Maybe it was the Chinese?  Maybe they got to the Americas not in 1421 like that book claims but 1500 years before.  Or maybe I should stop reading so much fantasy and watching movies like Thor and Superman.