<human>:  I have a question about the History of mathematical thought. Where did the idea of a number line come from?
<bot>: The idea of a number line comes from the Babylonian system of arithmetic. The Babylonians used a base 60 number system, which is why we use a base 10 number system today. The Babylonians used a base 60 number system because they had 60 seconds in a minute, 60 minutes in an hour, and 60 hours in a day.