Actually, "we" have a fairly good idea when the 115-140-or-so Pyramids were built. We also know a great deal about their construction — the engineers who built them couldn't help but bragging about it. What we don't know is the precise method for moving the blocks up the pyramid. The problem is that Herodotus claims that the ancients hadn't invented cranes, yet, so the pyramids (he's probably discussing the pyramids at Giza) had to have been constructed via a ramp. A damning piece of counterevidence to Herodotus' claim is that the shadoof predates the pyramids, so it's not too far fetched to imagine they might have had some piece of equipment like this.
What's missing is a definitive historical statement; remember, historians require written evidence. Most of our evidence for the building of the pyramids is archeological. The sorts of building devices needed for the pyramids would've been generally useful for all construction — so they wouldn't have been left to rot at the pyramid build site, but repurposed until destruction.
What's missing is a definitive historical statement; remember, historians require written evidence. Most of our evidence for the building of the pyramids is archeological. The sorts of building devices needed for the pyramids would've been generally useful for all construction — so they wouldn't have been left to rot at the pyramid build site, but repurposed until destruction.