Pi is an irrational number with an infinite amount of decimals. While 3.14 is good enough for high school students and most engineers often use 4.0 just to be sure, there are actually a lot of uses for the rest of the decimals, primarily in cryptography. These days we know pi down to tens of trillions of decimals, but not too long ago calculating a few dozen could literally take a lifetime.
Many people in history spent years of their lives calculating a few decimals of pi, using a method where a circle can be approximated by a many-sided polygon that can have millions of sides, becoming closer to closer to a circle. The last person to use this method is the 16th-century mathematician Ludulph van Ceulen who spent 25 years working on the problem, coming up with a polygon that had 0.5 billion sides and calculating its circumference to calculate pi to within 20 decimals and later expanding to 35.
This number was considered his life’s work and gave him great renown, especially because this level of detail was more than enough for any practical use. The number is also dubbed the Ludolphine number in his honor. 3.14159265358979323846264338327950288
Not long after this, in 1666, Isaac Newton found a new method of calculating pi that can be done in arbitrary precision, making the old method that Van Ceulen used obsolete. Fortunately, he did not live to see this.
After his death in 1610, this number was placed on his grave in the Pieterskerk in Leiden. The gravestone was lost over the years but restored in 2000. The monument can still be seen today, bearing the following roughly translated text: “Here lies buried Mr. Ludolph van Ceulen, professor in mathematics. Born on the 28th of January 1540, died on the 31st of December 1610. During his life, with lots of effort, he found that with a diameter of 1, the circumference is between 3.14159265358979323846264338327950288 and 3.14159265358979323846264338327950289”
Know Before You Go
The monument is found in the Pieterskerk. Entrance is 5€, sometimes free during open monument days. If you are there, don't forget to also visit Snell's grave (link).