Why Does the Great Pyramid of Giza Look Unfinished?
The physicist, John Zajac, wrote: "This protective covering was made up of...hard, white limestone, similar to marble but superior in hardness and in durability against the elements...The casing stones, 144,000 in all, were so brilliant that they could literally be seen from the mountains of Israel hundreds of miles away...The people of the area had viewed the pyramid and its polished stones with awe for centuries. But when a 13th century earthquake loosened some of these casing stones, the Arabs recognized a great quarry of pre-cut stones that could be used to finish off palaces and mosques. For instance, the casing stones were used to rebuild the new city of El Kaherah plus Cairo mosques and palaces, including the Mosque of Sultan Hasan."
Historically, this is standard Islamic operating procedure. Wherever Islam has established itself throughout the world, it has destroyed or defaced monuments that represented the previous (conquered) culture and replaced it with Islamic structures and mosques. Afghanistan used to be Buddhist. Turkey used to be Christian. Pakistan used to be Hindu. The former cultures and any symbols of them were annihilated and replaced by Islamic culture.