Olympic rebirth: Berlin's Olympic Stadium, long neglected for its historical associations, has been imaginatively and sensitively revived as the showpiece for this year's World Cup.

The Berlin Olympic Stadium has always been an extraordinary and contentious challenge for politicians, architects, engineers and athletes. The present stadium was conceived and masterplanned by Werner March between 1926 and 1933 on the site where his father Otto March built a track for horse racing at Kaiser Wilhelm's behest in 1909. Some years later, March senior received a further commission to design the so-called German Stadium in the middle of his racing track. Scheduled to host the ultimately abandoned sixth Olympic Games of 1916, it was the largest sports arena of its day with a spectator capacity of 30 000.

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After this false start, Olympic plans were put on hold until 1931 when Berlin was awarded the Games for a second time, but when the Nazis came to power in 1933, preparations assumed a new impetus. Hitler decreed that he wanted a completely new stadium that could accommodate both sporting competition and mass rallies for political and propaganda purposes. In response, Werner March conceived the Reichssportfeld, a sports complex of 117 hectares comprising a swimming pool, open air theatre, rally field, the German Sports Forum and, to crown it all, the new Olympic Stadium. Miraculously, the entire complex somehow survived both the Second World War and post-war occupation as a military headquarters by the British. Following their departure, it languished and suffered years of neglect.

In 1998, despite Berlin's failure to secure the 2000 Olympic Games, the Berlin Senate staged a competition to renovate the Olympic Stadium. German architects Von Gerkan, Marg & Partner (GMP) won first prize with a proposal which addressed the entire site, the only one of 57 national and international submissions to do so. With exemplary sensitivity, GMP's design combined the demands of a modern sports facility with the preservation of key historic buildings including that of the former Reichssportfeld.

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The main elements of the stadium's renovation and modernisation can be summarised as follows: repair of concrete structure, modification of upper tier and complete reconstruction of lower tier (adding 1600 extra seats), the sinking of the playing field by 2.65m, a new roof, modernisation of all technical and athletic areas, independent access to 100 VIP lounges and restaurant, underground car parking on two levels for 630 cars and underground warm-up tracks. All new and additional facilities were placed underground so as not to obstruct views. With remarkable candour and determination GMP have responded to the task of transforming the neglected Olympic Stadium into an ultramodern multi-purpose sports venue with a newly increased seating capacity of 76 000.

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The goal of the renovation work was to retain as much of the original building as possible and to restore the existing fabric. Thus each stone to be removed was registered and later replaced in exactly the same location. Special emphasis was put on the legibility of the historic elements; for instance, in the VIP lounges, new wooden panelling contrasts with the original stone cladding. For the athletes, the new fitout offers all kinds of indulgences. The greatest innovation is the 120m long indoor track in the warm-up hall near the Marathon Gate which can provide 'real' conditions' and is highly regarded in the sporting world. Mindful of the important role of the media in both reporting events and helping to propagate an image of the stadium, facilities are as media-friendly as possible with so-called 'mixed zones' where reporters and VIP guests can meet athletes for interviews. These are located next to the changing rooms and near the finish line. Additional press conference rooms are available on the lower levels and next to the press stands in the upper terrace.

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The crowning achievement, however, is the roof construction. The nature and geometry of the roof presented two challenges. First, it had to be as flat as possible, with masts and pylons avoided at all costs, so as to maintain the building's proportions and not obstruct the original facade. Second, with a historic urban axis running through the middle of the stadium, the roof had to remain open in front of the Marathon Gate, so could not be a closed ring. Both constraints were resolved by placing 20 steel tree columns (each 250mm in diameter) as high up in the upper tiers as possible. These prop up a series of new roof trusses that span 68m. Such an arrangement compensates for the missing tension ring due to the gap at the Marathon Gate. In section, each of the 76 roof trusses resembles an aeroplane wing wrapped in a translucent membrane and the inner roof edge is articulated in steel and glass. At night, the roof is transformed into a gigantic glowing organism and lighting scenarios include a spectacular 'ring-of-fire'.

Construction took just over four years from 2000 until 2004, from which time the stadium has been in regular use, for football matches and even a Rolling Stones concert. In July 2006 it will host the final of the World Cup and its triumphant public civic and sporting rebirth will be complete.