There is an irony here, however. The King's Library previously housed the collected books of George II and III - sold, not given, to it by cash-strapped George IV. At its inception, this early national museum was a museum of everything, and that included book-learning. This was the germ of what much later became the British Library, the centerpiece of which was the Round Reading Room dropped into the courtyard by Smirke's younger brother Sidney as early as 1857. The departure of the British Library to its new building in St. Pancras in 1998 freed up large chunks of the museum, allowing first the Great Court and now the Enlightenment Gallery to be created. There is still a slight sense of absence. The glass-fronted bookcases in the Enlightenment Gallery make for nice displays, but they are clearly meant primarily for books, and the Museum has duly sourced a supply of an appropriate age to fill them. So this is by no means an utterly faithful re-creation of what the space was originally like, for the simple reason that the contents are entirely different. They just happen to be the right period.

But then as the architects of the restoration, the American firm HOK, point out, the room itself is the primary exhibition. The container is more important than the contained. For this reason it is knocked about as little as possible. Yes, there is now air-conditioning and dainty fibre-optic lighting and writhing masses of cabling, but that is adroitly threaded behind the panels and through the staircases. All you see is the volume of the space and its rich palette of original materials: granite, alabaster, marble, scagliola, gilded ironwork: a feast of materiality.

I admit I was taken aback when I learned that the architects of the restoration were HOK. This is a giant international firm, originating in St. Louis, Missouri, best known for sports stadiums and airports. The thought of such an outfit getting to grips with the Grade I listed Smirke-designed receptacle of the nation's cultural patrimony would have been unthinkable a few years ago. But in Britain, HOK has gone native and acquired some serious cultural design expertise. Their all-new Darwin Centre at the Natural History Museum, for instance, is a worthy addition to that high Victorian Alfred Waterhouse building. It's a sign, if one was needed, of what is now the total globalization of the profession. London is the architectural crossroads of the world.