The mosque at Kew Gardens stood on a little hill, close to the Chinese pagoda and the Alhambra. Of these three imitations of global architecture created between 1758 and 1763 in Princess Augusta's landscaped gardens, only the pagoda, built in brick and wood at full size, survives. But what about the vanished mosque? To judge from an 18th-century engraving, it was closely based on the Süleymaniye in Istanbul. It is hard to imagine how such a pastiche would be received today. In the 18th century it was a sincere homage to a religion considered by intellectuals like Edward Gibbon to be far more philosophical than Christianity. The 18th-century Enlightenment was one of the great revolutionary moments in human history. It was a time when a culture - Europe's - subjected its deepest beliefs to irony and critique. The results of such radical thinking were mind-bogglingly disruptive. By the end of the 18th century, a European state would not just execute its monarch but abolish Christianity. In 1793, in the most extreme phase of the French revolution, the Bishop of Paris was forced to confess himself "a charlatan" and to declare that from now on "there should be no other public cult than liberty and holy equality". This movement now has a permanent display