Amidst earthquakes in northern Egypt, workers (perhaps the descendants of those who served Al-Mamun) stripped away many of the outer casing stones,[70] which were said to have been carted away by Bahri Sultan An-Nasir Nasir-ad-Din al-Hasan in 1356 for use in nearby Cairo.[96]
Many more casing stones were removed from the site by Muhammad Ali Pasha in the early 19th century to build the upper portion of his Alabaster Mosque in Cairo.[citation needed] Later explorers reported massive piles of rubble at the base of the pyramids left over from the continuing collapse of the casing stones, which were subsequently cleared away during continuing excavations of the site. Today a few of the casing stones from the lowest course can be seen in situ on each side, with the best preserved on the north below the entrances, excavated by Vyse in 1837.
The mortar was chemically analyzed[116] and contains organic inclusions (mostly charcoal), samples of which were radiocarbon dated to 2871–2604 BC.[117] It has been theorized that the mortar enabled the masons to set the stones exactly by providing a level bed.