Event
Seven Bridges of Königsberg
A historical puzzle about crossing each of a city’s seven bridges exactly once, whose solution founded graph theory.
Updated Oct 12, 2026 · 1 min read · 2 connections
- Solved
- 1736
- Solved by
- Leonhard Euler
- Location
- Königsberg, now Kaliningrad
The problem
The city of Königsberg sat on both banks of the Pregel River and included two islands, joined to each other and to the mainland by seven bridges. Residents asked whether one could walk through the city crossing every bridge exactly once.
Euler’s solution
Leonhard Euler reduced the map to land masses and the bridges between them, and proved that such a walk is impossible. A walk that uses every edge once exists only when zero or two vertices have an odd number of edges. The argument is regarded as the first theorem of graph theory.