Temple of learning

As for the project team and its Egyptian government backers, the building is being talked up as the architectural wonder of the 21st century, housing the foremost centre of learning in the eastern Mediterranean, just as its vanished precursor did in antiquity. Bilbao's new Guggenheim Museum and Sydney's Opera House are regularly invoked by the library's project director, Dr Mohsen Zafran, who envisages the library as the catalyst of urban regeneration for the run-down sea port and holiday resort of Alexandria.

On the other hand, the Bibliotheca Alexandrina has already been dubbed the Elephantina Albina, an Egyptian white elephant. Not only will the internet make traditional collections of books obsolete, critics argue, but the initial collection of 400 000 volumes will be too small to attract an large enough community of scholars to fill all 2500 reading places. At Bilbao, the development of the Guggenheim was paralleled by a comprehensive urban regeneration programme, of which there is little sign in the congested, decaying city of Alexandria. And as for the building itself, it is held up as Egypt's first "intelligent" building, one that will be reliant on a sophisticated facilities management operation, yet this is another activity little evident in Egypt.

It will take years, if not decades, to see which of these opposing visions proves to be correct. To date, it is the building rather than the institution that is having the most immediate – and powerful – impact. And seen as the result of an open international competition, it is a blazing and all too rare success. The competition was won in 1989 by a loose constellation of Norwegian, Austrian and American architects with no track record as a practice calling themselves Snøhetta (after Norway's highest peak). Amazingly, the building that is nearing completion on the ground is self-evidently the architect's competition-winning design.

The most jaw-dropping element in the building complex is the huge hall directly below the tilted disc. Here, all the library's reading rooms have been combined into one immense open-plan space stretching through the entire expanse of the 160 m diameter lid overhead. As big as New York's Grand Central Station, it is by far the largest library reading room in the world. The reading areas for the library's different departments are divided into seven terraces that cascade downwards below the sloping roof. Through these reading terraces rises a forest of cylindrical concrete columns, and daylight filters in through skylights that run diagonally between the columns.

There is no escaping the "wow factor" of this building, inside or out. However, the real richness and resonance of the architecture comes from the counterpoint between bold, sculptural geometric forms and mechanical modular repetition, and no less from the counterpoint between state-of-the-art functionality and timeless symbolism.

As Christoph Kapeller, Snøhetta's Austrian founding partner and project architect, explains: "We worked from the book outwards." The geometry of the building is primarily generated by the functional arrangement of bookshelves and reading desks into identical structural bays measuring 14.4 × 9.6 m. The 16.08° slope of the roof enables these bays to rise by a series of 4.15 m high stories.

This strictly functional grid is contained within a building perimeter in the symbolic shape of a circle. "The circle expresses the containment of all human knowledge," says Kapeller. In fact, the library is 11-storeys high and contained in a cylindrical envelope with an ovular cross-section. However, because the cylinder is tilted at an angle of 8.04° to the vertical, the floorplate and the roof form true circles for the horizontal floorplate and the roof plane. Like the British Library, completed in 1997, the bulk of the building is sunk underground to protect its precious paper freight from the external environment.

The bold geometry and symbolism have a strong impact both externally and internally. Approach the building from the corniche road along Alexandria's seafront and you find spread in front of you the huge, silvery, tilted disc of the lid to the elliptical cylinder. The disc rises at its low angle from below pavement level and is nearly surrounded by a pool of water. The effect is more like a ramped plaza than the building roof it actually is.

The disk is faced in silvery, smooth aluminium sheeting, and its top surface has been scalloped to create the 35 identical diagonal skylights lighting the reading room below. The aluminium-clad indents are softly moulded like aerofoils, and the diagonal skylights are shaded by curved glass eyebrows.

Kapella takes delight in describing the low, sloping disc as a "non-building", creating a gap, a breathing space, in the oppressive 13-storey wall of buildings that make up Alexandria's seafront. He explains that the silvery disc mirrors the glorious crescent-shaped sweep of water in the city's natural harbour. At the same time, he acknowledges other contrasting inspirations. It reflects the natural discs of the moon and sun rising slowly above the horizon – two of the oldest icons in Egyptian mythology. But the roof, with the repetitive aerofoil shapes of the indented skylights, is also unmistakably high-tech, for which Snøhetta found inspiration in that archetypal industrial component of the new millennium – a microchip wafer.

Approach the building from the hinterland and you are faced with another monochrome expanse, this time of the cylinder's perimeter wall as it rises above pavement level. Far from being a smooth, metallic, high-tech skin, this is a curving cliff face of roughly cleft grey granite, quarried in Aswan in southern Egypt. The only modulations in the granite cliff face are large letters that have been carved into its surface. The letters have been borrowed from as many of humankind's alphabets as could be found – an obvious reference to world literature.

Four other bold elements make up the external form of the complex. A large sphere faced in charcoal-grey glass-reinforced concrete sets off the flat disc of the library roof and contains a 120-seat planetarium. An open plaza has been formed between the new library and an eight-year-old concrete conference centre, which has now been incorporated into the new library complex. The side of the cylinder fronting the plaza has been cut off flat and faced in curtain walling to create the main entrance and restaurant for the complex. And a steel walkway picks its way at high level through the site from the seafront to the existing university behind the complex.

Internally, the great reading room hall is a truly mesmerising space. First, there is the drama of seven terraces that cascade down through the space. Then there are the 56 repetitive skylights that cover each structural bay. The skylights have been precisely orientated at the diagonal to face north and exclude direct sunlight – the enemy of books – while admitting glimpses of the blue Mediterranean.

Each skylight bisects its sloping roof bays diagonally between columns, and the lower lip of the roof has been gently folded downwards. To support these roof bays, the slender cylindrical concrete columns expand into elegant elongated conical capitals. Although simple in concept and identical in design, this repetitive grid of roof bays and columns builds up an extraordinary sculptural rhythm over the entire sloping roof plane, with each bay being slightly modulated in form by the varying vertical and horizontal angle of vision.

The combined effect is not so much that of a Western cathedral's linear nave and aisles, as of a gigantic mosque, such as the Mezquita in Cordoba, with a grid of columns stretching as if to infinity in every direction. Kapeller also acknowledges that the conical capitals bear a fortuitous resemblance to the carved marble capitals of Byzantium. The reading room also calls to mind the hall of columns of the ancient Egyptian temple complex at Karnak.

The new Alexandrian library is assured of being hailed by the international architectural community as a "contemporary classic", as Kapeller hopes. Whether its historic references will be enough to charm Egyptian visitors is another matter. Recognising that Egyptians have a weakness for gaudy baroque styling, Kapeller has added small panes of coloured glass into the monochrome roof to add splashes of blues and greens to the interior. For his part, director Zahran is confident that startling architecture will, in the long run, win public admiration, as has happened with the Sydney Opera House.

Whether the library will live up to its aspirations as an international centre of scholarship is open to question. The microchip wafer that inspired its disc-like form could yet become tragically prophetic by making its paper-based contents obsolete.