Dedicated to Sainte Osmanne, the 12-century nave is the oldest part of the church. The religious activity of Féricy was significant, the pilgrimage route to Saint James of Compostela was diverted to the town to venerate Saint Osmanne and her source (which was said to enhance fertility). Thus a Parisian workshop agreed to create, between 1532 and 1540, stained glass windows illustrating episodes from the New Testament and some hagiographic scenes of the patron saints of the church. Part of a bay of these windows was exhibited at the Louvre in 2017. The remarkable state of conservation and the artistic and iconographic unity of these stained-glass windows contribute to their exceptional value. Queen Anne of Austria had a mass celebrated in the church. On this occasion, water was brought to her from the Holy Osman Spring. After 22 years of sterility, she gave birth to the future King Louis XIV.