The twelfth-century lays of Marie de France are among the most popular of all medieval works and are a primary source of Arthurian material. For the first time, this analysis treats these poems as an architectural unit. The structure of these lays, written by the first poetess of the Anglo-French tradition, is linked through its thematic construction to the Church Fathers and the architects of the Gothic Cathedrals. Working from the British Museum’s Harley Manuscript 978, this study preserves the integrity of the original manuscript as well as its authorial purpose.