If you think that our tax is confusing, the ancient Egyptians had their own tax measuring stick, literally. The nilometer was used to determined your tax rate based on the rise and fall of the river Nile. American and Egyptian archaeologists have discovered a rare structure called a nilometer in the ruins of the ancient city of Thmuis in Egypt’s Delta region. Likely constructed during the third century B.C., the nilometer was used for roughly a thousand years to calculate the water level of the river during the annual flooding of the Nile. Fewer than two dozen of the devices are known to exist.