The Egyptians don't build the pyramids. Their rulers go straight to the non-pyramid tombs of later dynasties, or their bodies are floated down the Nile to the sea, or they have other ways to show grain, or the space aliens don't build them for them or whatever POD you want to use. No pyramids, just the normal temples and inscriptions you get with any other civilization of that level.
How does this affect the rest of history?