The ancient Egyptians, during the Pharaonic Period, began to measure the Nile’s water level in order to better predict the harvest.
A nilometer was a structure used by the ancient Egyptians to calculate the water level of the Nile River during its annual flood, and therefore predict the success of the harvest and compute the tax rate for the year.
This tradition can be traced back to over 5,000 years ago.
It was a step-like structure that measured how high the flood would be. If it was low, there would be famine. If it was too high, it would be destructive. There was a specific mark that indicated how high the flood should be if the fields were to get good soil.
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[Photo title by Prong hunter - via Wikipedia]