The Greeks probably used not only columns but also regular forms to arrange the stones. The numbers then were classified after the forms one could make of them: 4, 9, 16, ... were square numbers; 3, 6, 10, ... were called triangle numbers and so on. The root of a square number then is the numbers of stones at one side.

	Arithmetic and Weaving in Antiquity A pebble proof of the incommensurability in the square

	The Greeks probably used not only columns but also regular forms to arrange the stones. The numbers then were classified after the forms one could make of them: 4, 9, 16, ... were square numbers; 3, 6, 10, ... were called triangle numbers and so on. The root of a square number then is the numbers of stones at one side.