All of the finishing work is done by hand. Not saying it isn't labor intensive. Remember, these people could spend generations building these things. The bottom of the structure dates much earlier than later additions. The Coliseum was built in a fraction of the time and that mortar-less construction has massive amounts of force bearing down on the arches. Not to mention the mass of the crowd that it has to support which is a dynamic load as people are moving and jumping around in their seats during events. I think anyone that automatically thinks aliens is discounting the ingenuity of humans. Our intelligence is essentially the same as it was 5,000 years ago, only our available tools have changed. Quit trying to apply modern technology to buildings that weren't built that way. A massive crane might have a hard time lifting a 100 ton block but using ramps made from dirt, wood and stone will get the block up there as well, it just takes longer.