Musicus Online Museum

Clausula for St. Stephen: Video caelos

Clausula for St. Stephen: Video caelos (late 12th/early 13th century)


The late twelfth century and early thirteenth century witnessed a remarkable flourishing in liturgical vocal music at the famous Cathedral of Notre Dame in Paris. Many important technical developments occurred in the realm of rhythm, performance, and musical notation. Scholars have learned that much of the surviving repertoire from Notre Dame was part of the enormous Magnus liber organi (Great Book of Organum), one of the most important and earliest sources for written polyphonic music (i.e. for more than one independent voice) in the Western musical tradition.

This excerpt of music from that “Great Book of Organum” is a brief “clausula” for St. Stephen. A clausula is a self-contained section of two-voice polyphony, with a short segment of chant in the lower voice, with a newly added musical line in lively rhythmic patterns in the upper voice. In this case, the plainchant fragment (“Video”) is taken from the Alleluia chant for the Mass of St. Stephen (see full text below). Clausulas seem to have served a range of purposes in the early thirteenth century. They could be inserted into the performance of longer sections of chant, sung as self-standing items by clerics outside the liturgy, used as a site of compositional and notational experimentation, or set to different texts to suit various performance conditions.

Full text of the chant “Alleluia. Video Caelos”:

Alleluia. Video caelos apertoset Ihesum stantem

a dextris virtutis dei.


Alleluia. I see the heavens openedand Jesus standing at the right hand

of the God of Hosts.



Refers to this piece of MAG art: