Architecture: In the midst of a building blitz: With so much construction taking place, Berlin is almost as difficult to cross as in the days of the wall, complains Jonathan Glancey

There used to be just one Berlin wall; today there are many. The one we all knew and hated was built by Erich Honecker's 'working-class combat groups' at the height of the Cold War; the new walls are the products of crude capitalist development and government bureaucracy.

Honecker's wall (or 'Anti-Fascist protection barrier') divided Berlin from August 1961 until November 1989. It was possible for Berliners to cross from one side to the other during its unsightly life. They could apply for a visa and, if successful, shuffle through 'Checkpoint Charlie' on Zimmerstrasse. Or they could construct aircraft, dig tunnels, or, as several did successfully, insinuate themselves into the smoky interstices between the engines and exhaust pipes of bubble- cars thus escaping the scrutiny of border guards. Eighty Berliners were gunned down trying to cross from east to west.

No one shoots at you today, yet it remains difficult to cross from one side of the German capital to the other. The crossing can be done readily enough by U-bahn or S-bahn - the public transport network is linking up with what appears to be truly Prussian efficiency - but try walking and you will come up against one new wall after another.

Berlin's new walls are steel barriers erected by construction companies on behalf of the bulky business corporations that are parcelling what was no man's land and the streets flanking it into vast development plots. Try crossing Friedrichstrasse, a main street running parallel to what was the wall, on the east side of the city. Courtesy of Mercedes-Benz and other developers, you are checked from doing so.

Halfway along the street, a huge hole is surrounded by barriers higher than Honecker's wall. A building bigger than a Zeppelin hangar, but without the charm, is to rise here. It is sad to see the names of some of Europe's most imaginative architects tagged to the monster. Is that Jean Nouvel's name on the developer's board? Is the designer of the much-admired Institut du Monde Arabe in Paris really involved in such commercial bombast? Surely not; it must have been a trick of the eye, dazzled at night by searchlights mounted high on cranes surrounding the site.

Unable to cross here, you may try further up. A right turn at the top of the street by Friedrichstrasse station should take you to the wonderful cluster of shrapnel-ridden Neo-Classical and Baroque temples that culminates in Schinkel's exquisite Altes Museum. Instead, fences fight you all the way. You must make a long detour to reach the cultural glories of east Berlin. Perhaps not for ever, but the irony of these walls is not lost on Berliners.

Meanwhile, the cold heart of no man's land - Potsdamer Platz and Leipziger Platz (at the bottom of Friedrichstrasse) - remains a place, or rather non-place, where even Wim Wenders's angels might fear to tread. This is the biggest and potentially most profitable urban development site in Europe.

It is hard to imagine that Potsdamer Platz and Leipziger Platz were the Piccadilly Circus and Leicester Square of pre-war Berlin. Allied bombing and then demolition in 1961 (to give border guards clear lines of fire) did for the area. Today, a cluster of travellers' caravans, a row of single-storey shops and the remains of the once-opulent Hotel Esplanade are all that is left to the few pedestrians here of the urban razzmatazz revealed only in history books. These, and what looks like a prehistoric tumulus, but turns out to be the Fuhrerbunker.

The most important sight at Potsdamer Platz today is not that last primitive echo of the Reich, nor the remains of the wall that latter-day Elgins come to plunder. It is the prominent and floodlit developer's sign revealing Mercedes-Benz's mind-boggling plans for the transformation of the two squares and the nowhere land stretching from here up to the Brandenburg Gate.

Here, too, the scheme's main ingredients are office blocks and shops conceived on a Wagnerian scale. Again, the names of some of the world's best architects - Renzo Piano and Sir Richard Rogers among them - are emblazoned across the board, as if to say, 'Don't worry, this may be the mother of all redevelopments, but we promise style as well as scale.'

The quality of the architects charged with shaping the new Berlin is not in question. What is in question is the use to which this talent is being put. Berlin is in a hurry to become the seat of German government and the capital of Europe. But the ambitious transformation of Friedrichstrasse, Potsdamer Platz and Leipziger Platz calls to mind the excesses of London's ill- starred commercial property boom of the late Eighties. Think of Canary Wharf; Berlin has the chance to do much better than this.

Talking to Berliners, both east and west (the difference between the two remains enormous), you soon get the feeling that the city would be better off in the long run, physically and economically, if it were to be developed slowly and along more organic lines.

But this is asking too much; after all, the proposals for Friedrichstrasse and no man's land are very much in the tradition of Prussian planning. After the Napoleonic wars, Friedrich Wilhelm III stamped his authority on Berlin with squares, avenues and heroic Neo-Classical architecture. His favourite architect, Karl Friedrich Schinkel (1781-1841), happened to be a genius who, beside the Altes Museum and Schauspielhaus, also designed the Iron Cross medal and the Neue Wache, the war memorial and former guard house on Unter den Linden and the focus of anti-military protests over the past fortnight.

Albert Speer followed in Schinkel's bootsteps. His patron - an architect manque with designs on the world - wanted even bigger Neo-Classical monuments (such as a domed Volkshalle topping 1,000ft and so vast that clouds would form inside). Of that 'heroic' period in Berlin's history, few buildings have survived. These include the neo-Egyptian bunker built for the Gestapo on the corner of Albrechtstrasse and Reinhardtstrasse (now the 'Bunker' discotheque) and Goering's expansive Air Ministry that, almost wholly unscathed, bestrides a whole block at the southern end of Friedrichstrasse.

One cannot make direct comparisons between the urban dreams of Frederick III, Adolf Hitler and today's corporate giants, yet each had, or has, in mind over-scaled and ultimately insensitive redevelopment of a city that is - under its Prussian mantle - surprisingly higgledy-piggledy, watery and green (Berlin has more green space than almost any capital city, a forest of trees and, because of its many rivers and canals, more bridges than Venice).

Left to their own devices, Berliners have been reoccupying their once-divided city in gentle and romantic ways. The Globe Theatre, for example (occupying the remains of the Hotel Esplanade on Potsdamer Platz), with its adaptations of Shakespeare, flamenco, candle-lit bar and restaurant, is one of the most delightful evening haunts here or in any other European city. Yet, as the enthusiastic waiters will explain, the ramshackle and faded theatre will be blitzed next year as Potsdamer Platz is reborn as a daunting urban megastructure.

Throughout the city, but particularly in the east, bright young enterprises are taking short leases or simply occupying old buildings. They are making the city shine in a way that large corporations and their bombastic architecture never can. In the outskirts, for example, retailers are doing their worst, rushing up ugly superstores that make the nauseating and rapacious British breed almost palatable.

The plan by Christo, the Bulgarian-born artist, to wrap the Reichstag (Bismarck's parliament) next year is a delightful unofficial initiative that promises to lift the spirits of the city the artist has studied for more than 20 years. And Daniel Libeskind's Jewish Museum, a three-dimensional bolt of angular lightning, promises to be one of the most challenging and moving new buildings in Europe.

But the die has been cast. The centre of Berlin will become a showpiece, a meisterwerk of capitalist and governmental ascent. By the turn of the century, 100,000 civil servants will be at work in new offices designed by some of the most chic names in European architecture. A pinnacle of new skyscrapers will stamp its facade across Alexander Platz, showcase of Honecker's Soviet-inspired Berlin (the big statue of Marx and Engels is still here), and cast its triumphant shadow across Schinkel's Altes Museum. Berlin, walled in by 'fast-track' or blitzkrieg developments, is on the march again. How much more civilised the Berlin of 2000 would be if developers and politicians could learn to shuffle in soft architectural shoes. Schweine might fliegen.

(Photographs omitted)