Sainte-Chapelle

King Louis IX (later canonised as Saint Louis) commissioned Sainte-Chapelle in the 1240s specifically to house relics he had purchased at extraordinary expense from the Byzantine Emperor, including the Crown of Thorns — the relics reportedly cost roughly three times more than the chapel's own construction. Built in a remarkably fast four years and consecrated in 1248, the chapel was designed to make an architectural argument as much as a religious one: proof that Paris, and the French crown, could rival Constantinople and Rome in sacred grandeur.

The upper chapel is the reason to come: fifteen stained-glass windows, rising 15 metres and covering nearly two-thirds of the wall surface, depict over a thousand biblical scenes across some 6,458 individual panels, making this the largest and one of the best-preserved collections of 13th-century stained glass in the world. On a sunny day the effect is genuinely overwhelming — walls that seem to dissolve into colour and light, a design intended to evoke a jewelled reliquary at architectural scale.