"La Sainte-Chapelle ( The Holy Chapel ), is the only surviving building of the Capetian royal palace on the Île de la Cité in the heart of Paris, France. It was commissioned by King Louis IX of France to house his collection of Passion Relics, including the Crown of Thorns - one of the most important relics in medieval Christendom."
The Sainte-Chapelle or 'Holy Chapel', in the courtyard of the royal palace on the Île de la Cité (now part of a later administrative complex known as La Conciergerie), was built to house Louis IX's collection of relics of Christ, which included the Crown of Thorns, the Image of Edessa and some thirty other items. Louis purchased his Passion relics from Baldwin II, the Latin emperor at Constantinople, for the sum of 135,000 livres, though this money was actually paid to the Venetians, to whom the relics had been pawned. The relics arrived in Paris in August 1239, carried from Venice by two Dominican friars. For the final stage of their journey they were carried by the King himself, barefoot and dressed as a penitent, a scene depicted in the Relics of the Passion window on the south side of the chapel. The relics were stored in a large and elaborate silver chest, the Grand-Chasse, on which Louis spent a further 100,000 livres. The entire chapel, by contrast, cost 40,000 livres to build and glaze. Until it was completed in 1248, the relics were housed at chapels at the Château de Vincennes and a specially built chapel at the Château de Saint-Germain-en-Laye. In 1246, fragments of the True Cross and the Holy Lancewere added to Louis' collection, along with other relics. The chapel was consecrated on 26 April 1248 and Louis' relics were moved to their new home with great ceremony.
As well as serving as a place of worship, the Sainte-Chapelle played an important role in the political and cultural ambitions of King Louis and his successors.With the imperial throne at Constantinople occupied by a mere Count of Flanders and with the Holy Roman Empire in uneasy disarray, Louis' artistic and architectural patronage helped to position him as the central monarch of western Christendom, the Sainte-Chapelle fitting in to a long tradition of prestigious palace chapels. Just as the Emperor could pass privately from his palace into the Hagia Sophia in Constantinople, so now Louis could pass directly from his palace into the Sainte-Chapelle. More importantly, the two-story palace chapel had obvious similarities to Charlemagne's palatine chapel at Aachen (built 792-805) - a parallel that Louis was keen to exploit in presenting himself as a worthy successor to the first Holy Roman Emperor.