Richelieu visits Desargues visit at the fortifications of La Rochelle. Girard Desargues (February 21, 1591 - September 1661) was a French mathematician and engineer. He worked as a tutor and may have served as an engineer and technical consultant in the entourage of Richelieu. As an architect, he planned several private and public buildings in Paris and Lyon. As an engineer, he designed a system for raising water that he installed near Paris. His research on perspective and geometrical projections can be seen as a culmination of centuries of scientific inquiry, and going beyond a mere synthesis of these traditions with Renaissance perspective theories and practices. Desargues is considered one of the founders of projective geometry. He died in 1661 at the age of 70. Armand Jean du Plessis, Cardinal-Duke of Richelieu and of Fronsac (September 9, 1585 - December 4, 1642) was a French clergyman, noble and statesman. He was consecrated as a bishop in 1607 and was appointed Foreign Secretary in 1616. Richelieu soon rose in both the Catholic Church and the French government, becoming a cardinal in 1622, and King Louis XIII's chief minister in 1624. He remained in office until his death in 1642 at the age of 57.