Fighting as an engineer in Napolean's Grand Army against the Russians, I was injured, left for dead, captured by the Russians, and imprisoned from November 1812 until June 1814.
To help make time pass by as a POW, I taught geometry to my fellow prisoners...but only the geometry I could remember because I had no access to books.
I made two important contributions to projective geometry--the principle of duality and the principle of continuity.
In addition to developing the concept of poles and polar lines, I applied mechanics to more than double the efficiency of waterwheels.
My nemisis or rival in projective geometry was Joseph Diaz Gergonne, who claimed that he had discovered the principle of duality first---BUT HE WAS WRONG AS I FOUND IT FIRST!
Jean Victor Poncelet (1788-1867)