Pope Leo IX holds an Easter Synod to discuss the teachings of Berengar of Tours.
A French theologian and head of the school at the Chartres cathedral school, Berengar of Tours becomes important more because of the example he sets rather than because of any specific ideas.
Berengar of Tours believes that only rational understandings of revelation should be accepted and, moreover, that church leaders do not have the authority to compel anyone's assent to irrational understandings of revelation.
These ideas are too much for some, especially when they lead him to question the orthodox views about the Eucharist, and Pope Leo IX has Berengar of Tours excommunicated at this synod. It's not until 1078 that he is able to get a hearing from Pope Gregory VII, but he's forced to recant everything — not that he does so sincerely, but his life would be in danger otherwise.