Abbot Suger (c. 1081 – 1151), friend and confidant of French kings and Abbot of St Denis from 1122, began work around 1135 on rebuilding and enlarging the abbey to which he had been given as an oblate at the age of 10.
In his famous account of the work undertaken during his administration, Suger was careful to explain and justify his decision to rebuild the church, complaining at length about the parlous state of the old structure and its inability to cope with the crowds of pilgrims visiting the shrine of St Denis, particularly 
...on special days such as the feast of the blessed Denis [...] when the narrowness of the place forced women to run to the altar on the heads of men as on a pavement with great anguish and confusion.

Suger's fascination with light was not merely aesthetic.
Like many French clerics in the 12th century AD, he was a follower of Pseudo-Dionysius the Areopagite, a 6th-century mystic who equated the slightest reflection or glint with divine light.
When renovated, the Saint-Denis basilica included Suger's own words carved in the nave: "For bright is that which is brightly coupled with the bright/and bright is the noble edifice which is pervaded by the new light."

It is important to emphasise that Suger was the patron of the rebuilding of St Denis but not the architect, as was often assumed in the 19th and early 20th centuries.
In fact it appears that two distinct architects, or master masons, were involved in the 12th-century changes.
Both remain anonymous but their work can be distinguished on stylistic grounds.
The first, who was responsible for the initial work at the western end, favoured conventional Romanesque capitals and moulding profiles with rich and individualised detailing.
His successor, who completed the western facade and upper storeys of the narthex, before going on to build the new choir, displayed a more restrained approach to decorative effects, relying on a simple repertoire of motifs, which may have proved more suitable for the lighter Gothic style that he helped to create.
Abbot Suger (c. 1081 – 1151), friend and confidant of French kings and Abbot of St Denis from 1122, began work around 1135 on rebuilding and enlarging the abbey to which he had been given as an oblate at the age of 10. In his famous account of the work undertaken during his administration, Suger was careful to explain and justify his decision to rebuild the church, complaining at length about the parlous state of the old structure and its inability to cope with the crowds of pilgrims visiting the shrine of St Denis, particularly 
...on special days such as the feast of the blessed Denis [...] when the narrowness of the place forced women to run to the altar on the heads of men as on a pavement with great anguish and confusion.
Suger's fascination with light was not merely aesthetic. Like many French clerics in the 12th century AD, he was a follower of Pseudo-Dionysius the Areopagite, a 6th-century mystic who equated the slightest reflection or glint with divine light. When renovated, the Saint-Denis basilica included Suger's own words carved in the nave: "For bright is that which is brightly coupled with the bright/and bright is the noble edifice which is pervaded by the new light."
It is important to emphasise that Suger was the patron of the rebuilding of St Denis but not the architect, as was often assumed in the 19th and early 20th centuries. In fact it appears that two distinct architects, or master masons, were involved in the 12th-century changes. Both remain anonymous but their work can be distinguished on stylistic grounds. The first, who was responsible for the initial work at the western end, favoured conventional Romanesque capitals and moulding profiles with rich and individualised detailing. His successor, who completed the western facade and upper storeys of the narthex, before going on to build the new choir, displayed a more restrained approach to decorative effects, relying on a simple repertoire of motifs, which may have proved more suitable for the lighter Gothic style that he helped to create.
Basilica of Saint-Denis