The Sainte-Chapelle was built in fewer than seven years, between 1242 and 1248, for Louis IX. It was designed to house the Crown of Thorns and other Passion relics that the king had purchased from the Latin Emperor of Constantinople. Architecturally, it is the masterpiece of Rayonnant Gothic, the second phase of French Gothic, in which the wall plane is finally pushed to its theoretical limit.
The chapel is organised as two stacked rooms of identical plan but markedly different character. The lower chapel was reserved for the palace household and is consequently low and densely vaulted, with stout piers absorbing the load from above. The upper chapel, reserved for the king and court, is a single tall volume of roughly thirty-three metres in length and seventeen metres in height. Structurally it is a glass cylinder. Fifteen windows, each fifteen metres tall, occupy the entire length of its walls and depict 1,113 biblical scenes. The piers between them are reduced to slender bundles of colonnettes, the smallest stone elements that the loads will permit, and they are reinforced by iron tie-rods concealed within the masonry. This is one of the earliest structural uses of metal in Gothic construction, and without it the walls could not stand. The ratio of glazing to solid wall in the upper chapel is approximately three-quarters glass to one-quarter stone, which is the highest of any medieval building in France. The vaulting is quadripartite ribbing painted blue with gold stars, so that the ceiling reads as continuous with the sky.
The chapel was the architectural counterpart of the relics it housed. By acquiring the Crown of Christ, Louis IX was effectively transferring sacred legitimacy from Byzantium to Paris, and the audacity of the building was meant to read as evidence of divine favour. Embedded inside the Palais de la Cité, now the seat of the law courts, the Sainte-Chapelle is the rare medieval monument that survives almost intact at its original scale.