The "no slaves in ancient Egypt" line is a load of manure from the state propaganda apparatus. There was no choice in the matter, and that compulsion is the basis for the idea that the pyramids were erected by slave labor.
There's an idiotic claim that, because there are the remains of bakeries and cheap housing near the former construction site, means that there were no slaves. Do slaves go without food and shelter for 20 years? Of course not.
And your proof would be.....?
Actually, the whole idea that the pyramids were built with huge gangs of slaves yanking on ropes, and that they didn't have the wheel, or a simple lever-operated elevator, blah blah blah, is the big load of manure. The ancient Egyptians drilled holes in solid granite with helical tool marks that indicate a rate of advance of the drill (1:60) that is many times faster than modern machinery. To think these same people would employ forced gangs of slaves numbering in the hundreds of thousands (and the logistical and enforcement nightmare that goes with it) is amusing, to say the least.
Compulsion? Sure.
It was a civic/religious duty to continue the cycle of Life-Pharaoh-Egypt. Entire villages would be conscripted when they were idled by the Nile flood to work on the construction.
By comparison, in medieval times the commoners and the yeomanry would be called temporarily for the King's service. But you wouldn't call them slaves anymore then you'd call the present German or Israeli military conscripts a slave.