It is likely that Castellio read Calvin’s Institutes of the Christian Religion while he was still in Lyon. The Frenchman’s great work had been published first in Basle in 1536 and then three years later in Strasbourg. Castellio was so moved by what he read that he was determined to seek out the author in order to learn more from him; in May 1540 Castellio arrived in Strasbourg. 1 Calvin had returned to the city in 1538 following his expulsion from Geneva and was to remain until 1541.