La Saint Chapelle is a germ of Gothic architecture. It was built by the order of Louis IX (the Saint) to store the «crucifixion thorn of Jesus Christ». He brought it (or even bought) from Venice where it was moved from Constantinople.
In 1248 there were built and consecrated two churches, one above each other. The lower church served the foundation for the upper one. The design of walls was lightened as much as possible. The walls of upper church are made of mosaic windows. The height of each window is 15 meters.