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Studies of ancient bronze artifacts can be useful in understanding theprogression of human knowledge of mathematics and geometry. Here I discuss thedecoration 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 ofdiameters and distances of spirals, that the artist who made the decorationknew some approximations by rational numbers of the number pi, thedimensionless physical quantity representing the ratio of circumference todiameter.

Number pi from the decoration of the Langstrup plate