[OJFord]

Weren't pyramids built by slaves? Not necessarily disputing 'more spare time' (I don't know) but it's not really evidence of it is it?

[dagw]

Most modern historians seem to agree that they were mostly built by paid labor.

[MengerSponge]

I've read that pyramids were probably labor projects like the WPA or the CCC. The workers weren't slaves (they went on strike at one point), but they didn't have a ton of other ways to feed their families.