http://www.book-of-thoth.com/article1617.html

The classical story of the discovery of the upper chambers inside the Great Pyramid at Giza is well known. In the ninth century an Arab governor of Cairo, known as the Caliph al Ma’mun, decided to see for himself what lay inside the Great Pyramid (Khufu Pyramid) and began to excavate a tunnel bodily through the casing and core blocks with hammers and chisels. Fortuitously for the Caliph, their busy tunnelling shook the structure so much that the capstone fell off the end of the ascending passage.

The resonating crash was heard by the workers, who dug in that direction and found not only the descending passage, but also the ascending passage and all the upper chambers in the pyramid. After thousands of years lying undisturbed deep inside the Great Pyramid, the King’s and Queen’s chambers were opened at last and their treasure would soon belong to the Caliph.