Euler's Konigsberg Bridges

June 1, 1736

At twenty-nine, the Swiss mathematician Leonhard Euler solved the puzzle of whether one could cross all seven bridges of Konigsberg without retracing. He proved it impossible, and in doing so invented graph theory and topology. A problem that had amused tavern-goers became a foundation of twentieth-century computing. Euler himself went on to become the most prolific mathematician in history, publishing over eight hundred papers.