Tours de force.

The four glass towers of the French national library stand sentinel on the Parisian skyline. The forbidding exterior shields an abstract representation of a secluded cloister, an oasis for quiet study.

Cast as the protagonists in a new version of the hare and tortoise fable, the national libraries of France and Britain are nearing completion at roughly the same time. The British Library, beset by political and economic vicissitudes, has taken 36 years to build, while the Bibliotheque Nationale de Paris (BNP) propelled into life by the force of President Mitterrand's ambition, took less than 10 (AR July 1995).(1) The tortoise, the British Library, is now largely open (p34) except for the Science and Asian reading rooms; in Paris, the BNP's general reading rooms and public spaces are open, but the important reference libraries for researchers and scholars will not open until late this year.

The near coincidence invites comparisons. In terms of size, and sophistication, the French library claims to be comparable to the British. But except for sharing the mythic status of great libraries, and similarly housing the technologies necessary for modern storage and cataloguing, the character of the two new institutions could not be more different.

At the root of the differences are the approaches of the two architects. Colin St John Wilson, who is a subtle and complex architect, has designed his building from the inside out (externally the British Library suggests a large building trying to look smaller); Dominique Perrault has done precisely the opposite. His building with its massive stripped down forms the four glass towers, the immense bare podium built around a rectangular hole six storeys deep and containing a fully grown Normandy forest expresses grandeur, monumentality, and presidential ambition. In this scheme, as Perrault has explained, form does not follow function, it contains it. So there are some ill-fitting bits that seem capricious. It is not sensible, for instance, to store books in glass towers. whatever is said about the constraints of the Seine-side site, wooden shutters and solar glass. Nor is it considerate to make regular readers troop up the steps to the podium from the street and then make them descend into its bowels. This is a common complaint. The great wooden clad esplanade can be windswept and in wet weather extremely slippery.

But even before stepping onto the escalator that carries you down to the entrance you have been seduced by the emotional charge emitted by the building. Its external form, both forbidding and exhilarating in its enormous scale and Cartesian austerity, shields a rich and surprising interior.

The logic of concentrating library facilities and of removing auxiliary accommodation like offices to the peripheral towers is clear. Reading rooms - those for the general public in the upper levels, those for research below - and other constituents of the main library are arranged around the forest and in moving around the building you are nearly always aware of this astonishing green oasis. You enter the library at treetop level, passing through a set of modest sliding doors into a vast double-height entrance hall running 115 metres along the width of the building. Behind it are the conference rooms and at either end is access through and up and down to the reading rooms.

Equally logically, Perrault has imposed on each floor a consistent plan made up of concentric zones - like a rectangular onion. An outer technical belt providing the various services - the enormous book conveyors, lighting, heating, air conditioning, communication networks and so on - surrounds a zone of book stacks, with reading rooms giving on to an inner glazed promenade around the forest. The walkway was conceived as a cloister, though, oddly, readers cannot get into the garden, only gaze at its green and mossy perfection.

Separation of the envelope and its content, Perrault points out, allows the architect freedom to extemporize and accommodate volumetric variations on each floor, like the double-height entrance hall, the lofty reading rooms at the lowest level, or the more intimate reading rooms.

Richness derives from Perrault's use of materials, in particular wood and raw steel mesh, used in a manner reminiscent of '60s sculptors, Donald Judd and Richard Serra, to define, or create hierarchies of, space. The results are opulent in places, even medieval. Perrault loops rust-coloured mesh like chain mail across ceilings above wooden floors and rust coloured carpet, forms huge sheets of it into semi-opaque screens between book stacks and reading rooms and stretches fine metal webs across windows to soften light or across walls to attract it. Most spectacularly, metallic tapestries shimmering with light line the canyon walls of the deep escalator lobbies under each of the corner towers. Materials were chosen not only for their