Saint-Chapelle is two chapels built one above the other. The lower, a vaulted crypt dedicated to Our Lady, is a delight of plaster and paint hosting some of the oldest surviving wall paintings to be found in the city, although rather damaged by floods and its use as a grain store during the Revolution. Sadly the mystical effect of this space is today diminished by the siting of a large gift shop in the body of the chapel itself. But enough remains to imagine how it must once have looked, before removal of the altars and funerary slabs from the floor.
These days the upper chapel is reached by a narrow and unassuming spiral staircase in a shadowy corner of the crypt. It leaves visitors quite unprepared for what they are about to witness and the gasps are audible as successive climbers step out into the space above. Its dimensions are modest enough: 104 feet long, 34 feet wide, a single nave of four bays ending in a seven-sided apse. Nothing especially remarkable so far. But then we come to the statistic that truly marks out Sainte-Chapelle as a wonder of the world: 6,458 square feet of stained glass with barely a supporting pillar between each window. The upper chapel is an engineering marvel, a cage of shattered light in which words and numbers cease to be important. All we can do is stand in awe. We might be in heaven, or close to it, which was the intended effect. Because Saint-Chapelle was built for one purpose - to house the holiest relics in Christendom.
In 1239 King Louis IX of France, a young man not long come of age, newly married and with ambition aplenty, bought the crown of thorns of Christ's Passion. The seller, Baudouin II de Courtenay, the last reigning emperor of Constantinople, was in desperate straits touring Europe with a begging bowl to raise the cash needed to fund the defence of his realm. Louis paid a high price, one hundred and thirty five thousand livres, but it was an astute political investment calculated to make his seat of power a beacon of Christianity for centuries to come. For him personally it also secured canonisation, the only French king to achieve a place among the ranks of saints. Other relics were to follow, splinters and a nail from the True Cross. Louis spent a further one hundred thousand livres on a vast gilded reliquary to contain his precious purchases. Every year, on Good Friday, they were displayed by his priests in an act of solemn piety. 
Today the relics are gone, relegated to the treasury of Notre Dame a short walk away. Louis' expensive reliquary was unceremoniously melted down during the Revolution. But miraculously through all the nation's upheavals Sainte-Chapelle remains, its slender filigree steeple (the fourth in all) an elegant feature of the Parisian skyline. The stained glass has been officially declared a national monument inseparable from the architecture. During both World Wars the windows were taken down and they have been painstakingly restored, panel by panel, ever since.With binoculars, a detailed guidebook and plenty of time, it would be possible to pick out all the biblical and apocryphal stories told in every lancet and roundel, stories that would once have been understood by all without the need for such interpretation. But on a sunny day it is better to stand in the centre of this dazzling space and let the kaleidoscope of light play all around you. Perhaps I am not the average man-or-woman-in-the-street, but for me Sainte-Chapelle is the Parisian number one.
