The proposal by an Italian architect to build an alleged replica of the 18th-century Stadtschloss on its original site in Berlin raises questions about the authenticity of architecture that are relevant everywhere

Whether an alleged replica of the Prussian city palace in Berlin should be built or not may seem a remote, even irrelevant debate to us. But it raises the most fundamental questions about the issue of authenticity in architecture that transcend national boundaries.

The Prussian Stadtschloss stood on a site at the eastern end of Unter den Linden until it was badly damaged during the Allied bombing of Berlin towards the end of the second World War. In 1950, the ruins of the palace were demolished by the German Democratic Republic (GDR).

It was a vindictive act by the GDR authorities, who saw the Stadtschloss as a symbol of Prussian militarism. Eventually, in the mid-1970s, it was replaced by the Palast der Republik, with gold mirror glazing and a grand staircase lit by hundreds of pendant lamps.

The palast, in turn, became a symbol of the communist regime - second only to the Fernsehturm (TV tower) that could be seen from all over the city. It was also a building of social and cultural significance for many ordinary East Germans because of its use for civil weddings.

After the reunification of Germany and Berlin in 1990, the eastern sector of the city was effectively taken over by the westerners, and there was a determination to get rid of the Palast der Republik -because of what it represented - with asbestos cited as a pretext.

Thorsten Klapsch was the last photographer to capture its interiors before a prolonged period of demolition began. The canteen, bowling alley, congress hall, Cold War furniture and ancient computers were all still in place, sealed up in an atmosphere of "utter stillness".

It was condemned in 2002 with the idea of clearing space to rebuild a replica of the old Hohenzollern palace on the site - in revenge for its demolition more than 50 years earlier. Stripped down to its raw concrete, its last use was for East German agit-prop art exhibitions.

An international competition for the Stadtschloss project was won by an Italian architect, Prof Franco Stella, who's nearly 70; he proposed reinstating the Baroque facades of the 18th-century palace, working from old photographs of the building, and entirely different interiors.

Designed to provide additional space for Berlin's Humboldt University, it would be arranged around an atrium and two open courtyards in an architectural style that would not be out of place in Mussolini's magnum opus - the EUR quarter, on the south side of Rome. But the Humboldt Forum project has been stalled for lack of funding. Last June, the German government decided to postpone construction until after 2014, on financial grounds; this was hardly surprising in an era of austerity, given that it could cost as much as €670 million.

That's why there is now a travelling exhibition - currently on show at the Irish Architectural Archive on Merrion Square - and why fulsome endorsements have been obtained from the likes of Henry Kissinger, former president George Bush Senior and the World Jewish Council.

At the heart of the project, however, is the issue of architectural authenticity. What's proposed will not be the Stadtschloss inside and out, but a Baroque stone cloak over a contemporary building, however fascistic in style. It will be as "authentic" as anything in Las Vegas.

Stella, in his recent presentation at Trinity College, Dublin, cited the Custom House as a "precedent". But the truth is that the Custom House was never demolished. Although badly damaged in 1921 when the IRA set fire to it, most of the original structure actually survived.

As with the GPO and the Four Courts, which was even more damaged by shelling from Free State forces, the interiors date from the 1920s restoration of these great buildings and are of that period. But there is a historical continuity in terms of fabric, which will be absent in Berlin.

Other "precedents" cited by Prof Stella, such as Charlottenburg Palace in west Berlin and the Frauenkirche in Dresden, were also misleading. Charlottenburg was badly damaged by Allied bombing but not destroyed, while all of the Frauenkirche's stonework was preserved.

There is something very retrograde and deeply wrong about the Humboldt Forum project - especially for Berlin, which has been to the fore in championing the best of contemporary architecture through its international building exhibitions, stretching back as far as 1957.

To build a pastiche of the Hohenzollern Stadtschloss on the site of the Palast der Republik - which, whatever you may think of it, had authenticity - would add insult to injury. A new competition should be held to find an appropriate contemporary solution to this debacle.

The Berlin Palace-Humboldt Forum exhibition continues at the Irish Architectural Archive, 45 Merrion Square, Dublin, until February 15th