not many but for all that plastic we bury in landfills, so you reckon they built ramps a mile or more long and 150 metres high and did that for every block weight I forget weather 10 or 100 tons ? just not possible sure a group of people can lift a truck i did a similar thing once to shift a car we didn't have the keys for but to take a 10+ ton block up 150 metres and just say ooh they used ramps is pathetic, not to mention that they are placed with sub millimetre precision !