The Nilometer in Roda Island, Cairo, Egypt - an elaborate version of Roman and ancient Egypt Nilometers - dates back to 715 AD.
The Nilometer measured the water level of the Nile, and depending on the season, predictions to the water levels for the coming season could be issued. The central column is the measuring device, divided and graded into cubits.
An ideal flood filled the Nilometer to the 16 cubit mark; less could mean drought or famine and more could mean a catastrophic flood.
In many ways Egypt was ruled from this spot, it determined so much of Egypt’s economy, tax revenue and ultimately its governance. Because of this special status of this device in Egyptian society and economy, it was the site of one of the medieval world’s most lavish celebrations