This is very clever stuff. It recognizes an inescapable fact: all you have to do is wait long enough, and you make your own history. The British Museum has been around since 1753 and in its present building since that crucial date, 1827. At that time the museum's architect, Robert Smirke, gave his clients a space that is extraordinarily grand, even by today's standards. Right next to the huge bright volume of what is now the Great Court, you get what Smirke designed as the King's Library, the largest neo-classical interior in London. Taking up most of the east wing of the original museum, it was and is more than 300 feet long, 41 feet wide, and tall in proportion. Smirke, as much a master of new technology as of the Greek Revival style, confidently and invisibly used long concrete-clad cast-iron beams, allegedly fireproof, to make it so big. In its way it is an ancestor of the Pompidou Centre in Paris, another cross-disciplinary museum which uses similar structural techniques on a vaster scale. But any way you look at it, the former King's Library is a noble space. Now restored, this has become the Enlightenment Gallery.

An overt exercise in double coding is going on. The display in the gallery is all about the way collectors discovered and categorized the world in the 18th century. National museums across London have been ransacked, across all their public and reserve collections, to provide the material. But obviously this is more than just an exhibition about the historic period of cultural inquiry known as the Enlightenment. This is the museum examining its own origins. Accordingly it sets out to present the material much as you or I might have found it, had we wandered in one wet Tuesday towards 1830. This is all about old wooden floors and painted plasterwork and gilded railings and, above all, glass cases. You will not find computer terminals or giant plasma screens or kiddies' lift-the-flap interactive quizzes. You won't even find much in the way of labelling. The result is that the British Museum now contains a museum of itself, and for a very good reason: the BM is itself one of the great products of the Enlightenment. It deserves to be displayed.