The structural system of a building must be consistent with its appearance, and together they must reflect the function of that building. From an understanding of the geometry of 3-dimensional space arises the possibility of realizing these ideals as relationships within finished structures. We look back in time to see how the alliance between architecture and geometry has weathered the main periods of classical and European history. In particular we show convincing examples of the harmonious development of geometry and archltecture in the Renaissance, and of a serious rift which has developed between them since the 18th century