Gothic Rayonnant (Light)
Expansive interior light has been a feature of Gothic cathedrals since the first structure was opened. The metaphysics of light in the Middle Ages led to clerical belief in its divinity and the importance of its display in holy settings. Much of this belief was based on the writings of Pseudo-Dionysius, a sixth-century mystic whose book, The Celestial Hierarchy, was popular among monks in France. Pseudo-Dionysius held that all light, even light reflected from metals or streamed through windows, was divine. To promote such faith, the abbot in charge of the Saint-Denis church on the north edge of Paris, the Abbot Suger, encouraged architects remodeling the building to make the interior as bright as possible.
Ever since the remodeled Basilica of Saint-Denis opened in 1144, Gothic architecture has featured expansive windows, such as at Sainte Chapelle, York Minster, Gloucester Cathedral. The increase in size between windows of the Romanesque and Gothic periods is related to the use of the ribbed vault, and in particular, the pointed ribbed vault which channeled the weight to a supporting shaft with less outward thrust than a semicircular vault. Walls did not need to be so weighty.
A further development was the flying buttress which arched externally from the springing of the vault across the roof of the aisle to a large buttress pier projecting well beyond the line of the external wall. These piers were often surmounted by a pinnacle or statue, further adding to the downward weight, and counteracting the outward thrust of the vault and buttress arch as well as stress from wind loading.
The internal columns of the arcade with their attached shafts, the ribs of the vault and the flying buttresses, with their associated vertical buttresses jutting at right-angles to the building, created a stone skeleton. Between these parts, the walls and the infill of the vaults could be of lighter construction. Between the narrow buttresses, the walls could be opened up into large windows.
Through the Gothic period, thanks to the versatility of the pointed arch, the structure of Gothic windows developed from simple openings to immensely rich and decorative sculptural designs. The windows were very often filled with stained glass which added a dimension of colour to the light within the building, as well as providing a medium for figurative and narrative art.