Rawda Island Nilometer

This guide to the Rawda Island Nilometer in Cairo centers on a single number carved into a marble column deep inside this stone well: the flood reading that once decided how much of Egypt's population ate that year and how much tax every household owed. You'll hear how officials climbed a narrow staircase each day in flood season to watch the water creep up the column, and about the astronomer Alfraganus and the ninth-century caliph who ordered this structure built over an even older device. Look down the well shaft for the graduated markings that once made this reading possible.