Belem bastion.

Can a town be re-animated by a cultural centre? We went to see how Vittorio Gregotti's contribution to Belem near Lisbon is faring.

Belem is the little town on the north bank of the Tagus from which Prince Henry the Navigator's unbelievably brave sailors set out in tiny ships to discover what was in the world outside Europe. The early sixteenth-century Manueline architecture of the Jeronimos monastery was one of the results of the wealth they brought back from the Indies: an amazing, wildly optimistic cocktail of very late Gothic, proto-Renaissance and Oriental themes without parallel in the world then or since.

The monastery remains the centre of the town, which is now set in the amorphous matrix of the western suburbs of Lisbon. But its exuberant (much restored) main facade still looks over to the mighty river across a formal planted square, the Praca do Imperio. Today, the west side of this public space is defined by a building which is almost the total opposite of the Manueline one: Modern and secular, it is virtually undecorated; it stands on a storey-high, scarcely pierced plinth; its blank walls tell no stories, unlike those of the monastery, where the life of Christ and that of the burgeoning empire are intertwined; yet while the ecclesiastical building is self-contained and a glorious end in itself, the new complex is penetrable in many ways and is intended to be a small permeable chunk of city, with cross and through routes like the little streets of all southern European towns.

The Belem cultural centre by Vittorio Gregotti consists of three main elements, reading from west to east: a museum and library; a theatre complex; and a conference centre (intended to be largely used for cultural affairs - but as usual with such places, not always so). A further stage has been planned to the west with a square dominated by a hotel and shopping leading to a new street of shops, housing and miscellaneous functions.

What we have now is a big cultural plant, made originally for the 1992 rituals of the European Community, when Portugal was in the chair. Today, the building remains as a much used and cheerful part of what could clearly be a new lively and integrated part of the town, but partly because the final phase of the complex has not been built (city and national funds have been diverted to the 1998 Expo site up the river east of the city), the cultural centre is rather isolated.

Yet when we visited it in the twilight of a warm evening, the internal open spaces were full of families taking their passeggiata, interwoven with children amiably swarming about on skateboards; the cafes were cheerful; the bookshop was crowded; the museum well attended. The rough hand-tooled limestone panel walls were admirably free of graffiti; the public spaces remarkably clean and neat. Clearly, the complex works at quite a lot of levels.

The urbanity is perhaps partly due to the politeness and polity of the Portuguese, who to the more individualistic Protestants of the north seem paragons of propriety. But surely it is also a reflection of the parti. A main east-west axis unites and relates the different functional zones of the scheme at first floor level over the plinth which is much occupied by car parking. The axis is approached from the square in front of the monastery through a central opening on the ground floor in the middle of the east elevation of the new building. From here by dexterous juggling of levels, you can walk up to the eastern court of the axis, a quite narrow public open space which is intended to be surrounded by shops. Ascent to the court is under the main foyer of the congress centre which is normally approached up ramps on each side of the central entrance.

This east court is connected to the west (museum) one by the glazed foyer of the two theatre spaces: a 1500 seat auditorium to the north which is capable of mounting opera, and a smaller, flexible experimental theatre on the south. The museum court which follows is a good deal wider and is a much more cheerfully generous social space. On its north side is a wide trench, almost like the trace of a forgotten moat in a medieval castle; it brings light down to the extensive temporary exhibition spaces within the plinth. A bridge crosses the moat to ceremonially deliver you to the museum, in which white galleries play on three levels.

The main axis is crossed by two smaller open routes - alleys which run up north-south ramps on each side of the theatre complex to meet the main public promenade on top of the podium. These moves, like all the others in the complex, are intended to evoke the nature of southern European urbanity. Up to a point, it all works. The little north-south alleys in particular draw you in and up to the public open spaces. It is a great pity that the shops and little uses that Gregotti wanted to create at that level have not been realised.

The building breaks down towards the south in a series of planted terraces which evoke the delicious semi-tropical formality of traditional Portuguese gardens and offer wonderful views over the Tagus; northern green terraces look to the monastery and the little houses of Belem. What Lasdun has called 'levels of raised ground' have been created, both as landscape and parts of city.

Despite this, the complex provokes many questions. It sits mute and inarticulate against the wild exuberance of the Manueline monastery. Is a democratic monument bound to be so austere and uncommunicative? Why is it so detached from the texture of the town? Did the organisation have to be quite so diagrammatic? Why put the main new public open spaces a level above the square, and not dig the contents of the plinth below ground level, allowing much easier access and integration with the urban fabric? Where it makes gestures, the building is often ungainly: think for instance of the clumpen fly-tower of the main theatre, the really dull glass curtain walls, and the squashed ceremonial arched links between parts of the main axis.

Yet it suggests a notion of urbanity, and (so far) has worked well. The attempt is brave, and a part of the immensely difficult effort to find for our times a series of places as generous and humanly rewarding as those of the Jeronimos monastery. Their beauty was made out of a lost common spirituality - and of the violence and rapine of the Portuguese empire. Gregotti has tried to show how decency and figure might be attained in a generous democratic society.

Architect Gregotti Associati International, Milan

Associate architect Risco, Manuel Salgado

Project team Spartaco Azzola, Marino Fei, Sergio Pascolo, Paulo Albuquerque, Vitor Alves, Rita Amado, Jose Araojo, Lourdes Bispo, Judice da Costa, Carlos Cruz, Diogo Veiga da Cunha, Cristovao Macara, Jose Carlos Monteiro, Lino Ramos, Rui Ruivo

Structural engineer Segadaes Tavzres

Services engineers Ansaldo, Joule, Grade Ribeiro, Amman Progetti

Theatrical plant Heinz Oechslin

Acoustics Pedro Martins da Silva

Lighting Piero Castiglioni

Interiors Daciano Costa

Photographs Mimmo Jodice