The oldest written numbers, that you have found, were around in Egypt and Mesopotamia 3000 v. Chr. second hand; these peoples, who lived far apart, independently developed a series of numbers. Your simple numerals, 1,2 and 3, were imitations of the sticks and notches of the cavemen. It's interesting, that in many number systems, found all over the world, the 1 as a single dash (according to the stick) or as a point (Kieselstein) is written.