Number pi from the decoration of the Langstrup plate
  Studies of ancient bronze artifacts can be useful in understanding the progression of human knowledge of mathematics and geometry. Here I discuss the decoration composed by several circles and spirals of the Langstrup belt disk, an artifact of the Bronze Age found in Denmark. I am showing by measurements of diameters and distances of spirals, that the artist who made the decoration knew some approximations by rational numbers of the number pi, the dimensionless physical quantity representing the ratio of circumference to diameter. 
Amelia Carolina Sparavigna
physics.pop-ph