sea mirror of circle measurements

Borgesian poetry found on page 290 of George Gheverghese Joseph’s book “The Crest of the Peacock, The Non-European Roots of Mathematics”, in the section on Chinese Mathematics. He is writing about the “Ce Yuan Hai Ying” (“The Sea Mirror of Circle Measurements”), written by Li Ye between 1233 and 1248:

“This is a book in twelve sections involving 170 problems all telling the same story (relating to the same diagram, a circle inscribed in a right-angled triangle) of people wandering along certain roads around a circular town. Each person tries to catch sight of one another or of a given object such as a tree, which is hidden from them by the town walls. The question is invariably to find the diameter of the town, given the distances they have walked, and the answer is often the same: 120 bu (appr. 200 meters).”