In this picture we can appreciate the pyramid of Kefren. Originally, the whole pyramid was covered with a material like the one we can appreciate; in its originally state it was totally white and shining under the sun, giving the whole structure an impressive aspect.
However, this lustre was not lost due to decay, but by the hand of humans: air pollution is degrading it, and only the top of the pyramids still have this material. The rest was stolen thorough the centuries, and what remains was probably left because robbers lacked the skills to take it out from where it still stands.
This oddly means that fear and lack of knowledge sometimes may be useful to preserve relics and works of art.