Robert explained how much simpler it was to pay money for things than to exchange them as the people were doing in the market. Later on the soldier gave the coins to his captain, who, later still, showed them to Pharaoh, who of course kept them and was much struck with the idea. That was really how coins first came to be used in Egypt. You will not believe this, I daresay, but really, if you believe the rest of the story, I don't see why you shouldn't believe this as well.