Before 2500 BC, Sumerians had mastered the calculation methods of four arithmetic problems and worked out multiplication tables, square tables and cubic tables. Because of the frequent measurement of land, the Babylonians also mastered some geometric knowledge, and divided irregular fields into different rectangles, triangles and trapezoids to calculate the area. They also mastered the Pythagorean theorem and found that the ratio of circumference to diameter was 3. In algebra, they can solve three unknown equations. In addition, due to the need of trade, the Babylonians also formulated units of calculation for weight, length, area, volume and currency. It is no exaggeration to say that Babylonians were the most accomplished mathematicians in ancient times.