Mathematician, born in Lyon, SC France. By 1626 he was in Paris, and took part as an engineer in the siege of La Rochelle in 1628. He founded the use of projective methods in geometry, inspired by the theory of perspective in art, and introduced the notion that parallel lines "meet at a point at infinity'. His work on the ections of a cone greatly influenced Pascal. From 1645 he began a new career as an architect in Paris and Lyons.