King Louis IX commissioned Sainte-Chapelle within the royal palace on Paris's Île de la Cité to house relics of Christ's Passion, above all the Crown of Thorns acquired from Constantinople. Built rapidly in the 1240s and consecrated in 1248, the chapel presented the French king as a privileged guardian of sacred history. Housing the relics cost far more than constructing their architectural shrine. Ceremonies around them linked personal devotion, Capetian monarchy, crusading ambition, and the political claim that Paris had become a new center of Christendom.

The building has two levels. The lower chapel served palace personnel, while the soaring upper chapel was reserved chiefly for the king, court, and relics. Slender masonry supports frame fifteen tall stained-glass bays so that colored light dominates the room. More than a thousand scenes trace biblical history from Genesis through the arrival of the relics in Paris. Sculpture, painted surfaces, metalwork, and glass formed a unified program. The architecture became an influential expression of the Rayonnant Gothic pursuit of lightness and visual continuity.

After the royal court moved from the medieval palace, judicial and administrative institutions occupied the complex. Fires, floods, and alterations damaged the chapel over centuries. During the French Revolution, the treasury was dispersed, relics moved, sculpture mutilated, and the building used for archival storage. Much glass survived because tall cabinets stood in front of it, although panels were lost, rearranged, or replaced. The Crown of Thorns eventually entered the treasury of Notre-Dame rather than returning to its original shrine.

A major nineteenth-century restoration began in the 1830s under architects including Félix Duban, Jean-Baptiste Lassus, and Émile Boeswillwald. Their work repaired structure and glass, recreated sculpture and painted decoration, and added the present spire. It was both a pioneering conservation project and a forceful interpretation of the Middle Ages. Later campaigns have cleaned and protected the stained glass from pollution and condensation. The French state owns the monument, which is administered as part of the former royal palace complex.

Sainte-Chapelle can look astonishingly complete, but visitors encounter a mixture of thirteenth-century fabric, rearranged medieval glass, nineteenth-century reconstruction, and modern protective systems. Its authenticity does not depend on pretending those layers are identical. The chapel remains one of the clearest surviving statements of sacred kingship and Gothic design, while its revolutionary damage and restoration reveal changing French attitudes toward monarchy and heritage. The contrast between the more solid lower level and luminous upper chapel still communicates the social hierarchy and ceremonial purpose embedded in the original plan.