In the study of ecclesiology it is often said that the first treatises on the Church were written during the controversies around the bull Unam sanctam (1302) of Pope Boniface VIII. These works and their successors provide a political and institutional ecclesiology determined by the author's attitude to the papal claims. Before the bull, however, a friend of Boniface, William Durandus of Mende, wrote a commentary on the liturgy that summarised a very different ecclesiology which has its roots in the New Testament and the Fathers. The first book of his Rationale divinorum officiorum draws on previous tradition and uses the methods of spiritual exegesis of the Bible to provide a balanced ecclesiology from a 'reading' of the church-building. The wide circulation of the Rationale in late medieval and early modern Western Europe ensured that this traditional ecclesiology was quietly handed on, but modern writers have ignored it. A study of Durandus's interpretation of a church enables us to retrieve this tradition and suggests a new narrative for the history of ecclesiology.