In ecclesiastical circles Galileo’s explicit advocacy of the Copernican cosmology aroused the fear that error might be demonstrated in the Holy Scriptures, which clearly stated that the Sun moved. Especially among the Dominicans in Florence, alarmed voices were raised, resulting in a denouncement to the Holy Office. Urged to explain himself, Galileo entrusted to some private papers, never published, his idea of a relationship of mutual non-interference between theology and natural philosophy. In three letters addressed to Benedetto Castelli, Piero Dini and Cristina of Lorraine, he attempted to demonstrate that the Copernican position could be reconciled with the Holy Scriptures (which, unlike its interpreters, cannot be subject to error). He also called for separation between the sphere of theology, entirely spiritual and moral, and that of philosophy, centred on the search for natural truth. But all of Galileo’s efforts were in vain, and the concept of a mobile Earth was prohibited by the Holy Office as false doctrine.