The numbers we all use always (1, 2, 3, 4, 5, 6, 7 8 , 9 and 0 ) are known as "ARABIC " numbers to distinguish them from the "Roman Numerals" (I, II, III, IV, V, etc). Actually the arabs popularized these numbers but they were originally used by the early Phoenician traders to count and keep track of their trading accounts.
Have you ever thought why ? 1 means "one", and 2 means "two"? The Roman Numerals are easy to understand but what was the logic behind the Phoenician numbers?
It's all about angles ! It's the number of angles. If one writes the numbers down (please see the figure) on paper in their older forms, one quickly sees why. Angles have been marked with "o"s.
No 1 has one angle.
No 2 has two angles.
No 3 has three angles.
No. 4 has four angles
And so on……. and "0" has no angles