This chapel was commissioned by Louis IX the Saint to house the Crown of Thorns. The king bought the relic in Venice in 1239, where it was brought from Constantinople. The creator of the chapel, Pierre de Montero. decided to build two churches, one above the other, and both were consecrated in 1248. in 1248. The lower church serves as a high base for the whole structure, from which the colossal windows rise upwards. colossal windows rise up from it, ending in lancet turrets.
The steeply sloping roof is adorned with a light, graceful marble balustrade, and this exquisite architectural element is crowned by an openwork, upward-facing spire. 75 metres high. On either side of the façade rise two other towers with spires spires; in front of the façade - a portico, above which a large window-socket, dating from the XV with scenes from the Apocalypse.
The lower church, small in height - about 7 metres, consists of three naves, but the main nave seems huge compared to the side aisles. Decorative arches in trefoil-shaped arches resting on graceful columns run along the walls. The apse at the at the back of the church has a polygonal shape. This part of the chapel was intended for servants, while the luxurious upper chapel, accessed by a narrow spiral staircase. narrow spiral staircase, was frequented by members of the royal family and their courtiers.
The upper church has one huge nave, 17 metres wide and 20.5 metres high. The whole church is flanked by a high plinth with openwork marble arcades, interrupted by deep niches. In the third aisle are two niches, reserved for the king and his family. At each pilaster are statues of the apostles, dating from the 14th century. The structure has been lightened as much as possible in order to leave more space for the 15 huge stained glass windows, some 15 metres high, which date back to the 13th century, contain 1,134 scenes and cover an area of about 600 square metres. square metres. They depict biblical and gospel scenes in bright "flaming" colours. biblical and evangelical subjects.
