**The magic of π from its origins to the present day.**

**1 π permeates our existence,** well beyond the problems of geometry at school, where it is known as the ratio of the circumference to the diameter of the circle (or the area of a circle with a radius equal to 1). From electromagnetism to quantum mechanics, π affects many sectors. For example, it has to do with the Heisenberg Uncertainty Principle, it comes into play in the period of oscillation of the pendulum (which is proportional to our irrational number), as well as in the Coulomb force between two electrically charged objects. But the history of π is about 4 thousand years old. It was the Babylonians, great mathematicians, and architects, who first employed it, interpreting it as 3.125.

**2 Then the Egyptians came.** In an Egyptian papyrus of the seventeenth century. A. C. was approximated to 3.1605.

**3 The Greeks used polygons tangent internally and externally to a circle**, that is, respectively, inscribed and circumscribed (see graph above). The length of a circumference is in fact necessarily included between an upper and a lower limit, represented respectively by the perimeter of the external polygon, which is slightly larger, and the internal one, which is slightly smaller. The more sides a polygon has, the more precise is its approximation to the circle, and consequently the greater the precision with which one can obtain the number that links the circumference to its diameter. Archimedes of Syracuse (287-212 BC) used polygons with 96 sides. His conclusion was that the circle number must be smaller than 3+ (1/7) but larger than 3+ (10/71). Representing the intermediate value between the two with a decimal number was not yet within the reach of the Greeks, but the result would have been 3.1419. It has three digits correct after the decimal point and is only 1% different from today’s value.