Bonaventura Cavalieri was born in 1598 in Milan, Italy. He studied theology and became a member of the order of the Jeusati. He served as deacon in the monastery in Milan and later as prior of St. Peter's Church in Lodi. Cavalieri was appointed to the chair of mathematics at the University of Bologna in 1629. He died on 30 November 1647 in Bolgna.
Cavalieri's mathematical work served as a precursor to the calculus. He computed areas of plane regions by considering them as composed of infinitely many parallel line segments, and volumes of solids by considering them as composed of infinitely many parallel plane regions. He is best known for the principle that states that two plane regions with the same cross-sectional lengths must have the same area, and similarly that two solid regions with the same cross-sectional areas must have the same volume. Now Cavalieri's principle is recognized as a special case of the theorems of Guido Fubini and Leonida Tonelli that equates the double integral with the corresponding iterated single integrals. In addition to mathematics, Cavalieri worked on problems in optics, particularly the design of mirrors.