climate and geography: Egypt 241 As the Sahara dried out between 3000 and 2000 b.c.e., the Nile River valley became a center for human civilizations, including those in ancient Nubia With the invention of the Nilometer the Egyptians could record the river levels and attempt to predict their crop yields A Nilometer consisted of a series of steps that were used to mark the height of the Nile inundation as well as regular water levels Surviving Nilometers exist at the sites of Philae, Idfu, Isna, Kom Ombo, Dendera, and Aswān In Cairo there is also an Islamic Nilometer from about 705–715 c.e., which may have been built on the site of a Pharaonic Nilometer LOWER EGYPT The ancient capital of Memphis (modern Cairo) sits at the apex of the Nile Delta The delta, or Lower Egypt, is wide and