The Nilometer at Elephantine Island, in Aswan was used since the Pharaonic Era to measure the water level of the Nile, up to the nineteenth century, thus allowing the determining of taxes the farmers had to pay and take measures in case of high or low floods. The Nilometer was always annexed to temples and only priests and kings and nobles were allowed to enter it. Just beside the Nilemeter, The Tropic of Cancer passes.