Our tourist guide in Saqsaywuaman told us that the Incas would use criminals, rebels and generally non-conformist members of society as slave labour to build their fortresses and temples.
The workers had a plentiful supply of coca, of the local alcoholic spirit, and there was always music to keep time and energy. No-one really complained or felt dissatisfied with this life, she suggested. It was just like a party ...
Hmmmm ... Well, it's an alternative :-)
Apparently building StoneHenge was a party too :