Ancient Egypt was an essentially one-dimensional country strung out along the Nile, which flows from south to north. The winds were conveniently arranged to be predominantly northerly. To go north, a traveler could let his boat drift, while with a sail he could move south against the slow current. For this reason, in the writing of the ancient Egyptians, ‘go downstream (north)’ was represented by a boat without sails, and ‘go upstream (south)’ by a boat with sails. The words (and concepts) or north-south and up-downstream became merged. Since the Nile and its tributaries were the only rivers known to the ancient Egyptians, this caused no difficulties until they reached the Euphrates, which happened to flow from north to south. The resulting confusion in the ancient Egyptian mind is recorded for us to read today in their reference to ‘that inverted water which goes downstream (north) in going upstream (south).’

— P.L. Csonka, “Advanced Effects in Particle Physics,” Physical Review, April 1969, 1266-1281