The story of 十

ten

十 depict a rope with a knot on it, ancient Chinese used such symbol to represent the number of ten, since the number of ten is the largest number which human being can count by his both hands, it is a natural arithemtical unit, also, in the concept of ancient Chinese, a knot in a rope(繩結) means an end of a rope, so a knot in a rope is used to represent the number of ten. On the other hand, 廿(twenty), 卅(thirty) and 卌(forty) depicts two, three and four knots in a rope respectively.