Bonaventura Cavalieri refined early Greek work on the concept of indivisibles. His work served as a stepping stone to the concept of infinitesimals and was the foundation of Isaac Newton's development of the calculus. Cavalieri was born in Milan, Italy, in 1598. His actual birth date is uncertain; even his first name is unknown, because he entered a monastic order at an early age and adopted the first name Bonaventura as his religious name.

Cavalieri entered the Jesuatis (a Roman Catholic order founded on the rule of St. Augustine and not to be confused with the Jesuits or Society of Jesus) and took minor orders in 1615 at a monastery in Milan. In 1616, he transferred to a monastery in Pisa, where he met Benedetto Castelli, a former pupil of Galileo. Castelli introduced Cavalieri to the study of geometry and later introduced him to Galileo himself. From that point on...