From plainchant via simple 9th-century harmonies and the virtuosic duets of Master Léonin (known as organum), this hauntingly beautiful sequence charts the birth of polyphony up to the first music in four independent parts – composed by Master Pérotin and sung during the liturgy at the new Cathedral of Notre-Dame in Paris. From the official laying of the cornerstone in 1163 to the completion of the famous Western façade almost a hundred years later, Notre-Dame was the fertile home of singers and composers whose extraordinary handiwork has come down to us in the magnus liber organi: the “Great Book of Organum”.