Pyramid of Khafre, Giza Plateau

It looks like the syenite casing stones around the base (pink – outer layer) weren't original but were added later by someone who wanted to preserve as much of this ancient structure as possible.

Given this job today an engineer would simply cut the odds and ends off of the original structure and produce a flat surface, then butt the new syenite casing stones up against it.

Instead of this, the stonemasons of the time chose a much more difficult way around and painstakingly shaped each casing stone to fit the existing weathered and eroded profile.

The only other explanation is that the syenite casing stones were somehow softer at the time they were installed and the engineers simply pushed them into the original irregular profile, then let them 'set'.