Where this game comes from
The seven bridges of Königsberg
Königsberg (now Kaliningrad) had seven bridges joining two river banks and two islands. People asked whether you could walk across every bridge exactly once. Leonhard Euler showed it cannot be done, in a paper he read to the St Petersburg Academy on 26 August 1735.
One thing to hold: A map with the land squeezed down to dots and the bridges to lines — the first drawing of what is now called a graph.
Why it matters: Euler found the rule that settles every such map: a walk over each line once needs zero or two dots with an odd number of lines. Königsberg had four.
What we don’t know: The journal volume is dated 1736, but it did not come out until 1741, and Euler’s own letters about the problem are from 1736 — so exactly when he first heard of it is not certain.
Dates:
- 1735 Euler reads his solution to the St Petersburg Academy.
- 1736 He writes about the problem in letters; the journal volume carries this date.
- 1741 The paper is published.