Antonio Castelli was born in Brescia, Italy, in 1578 and took the name Benedetto upon entering the Benedictine order in 1595.
It was this occasion that prompted Galileo to write a long letter to Castelli on the subject of science and religion, which was later expanded into the Letter to the Grand Duchess Christina.
Both versions of the letter circulated in manuscript, and the Letter to the Grand Duchess was printed in Strasbourg in 1636.