Can harmony and beauty be captured in architecture? The author provides answers to this question that stem from a completely new research method - metrology. Musical intervals can be represented as proportions, and so can relationships in architecture. When defined criteria of accuracy reveal correspondences between music and architecture, harmonious relationships emerge. The Pythagoreans calculated them. The Roman architect Vitruvius demanded them for the representation of architecture, as did his Renaissance colleague Alberti. This sets the stage for the Middle Ages, whose architecture can be demonstrably embedded in music. Ultimately, according to tradition, Gunzo, the founding abbot of Cluny, was indeed a musician!.