The estimated cost of renovation and expansion of Berlin’s Pergamon Museum has almost doubled to €477 million ($526 million) above the initial estimate of €261 million ($288 million) due to unforeseen construction complications. Meanwhile, the date of completion has been pushed back four years, to 2023.

The reason for the enormous miscalculation is the discovery of a massive underground concrete caisson which was used to pump away water to allow for the steel foundations to be laid during the building’s initial construction between 1910 and 1930. The solid concrete structure should have been torn down after the foundations were put in place, but it wasn’t.

“The old pumping station discovered under the earth was not included in any historic blueprint,” Petra Wessler, president of the federal office for building and regional planning told the German daily Der Tagesspiegel. 

The canal surrounding Berlin’s Museum Island. Photo: Thomas Wolf via Wikimedia Commons.

Unfortunately, the huge concrete block now stands in the way of planned “Archaeological Promenade” which was conceived as a way to link the different buildings on the Museum Island to one another.

In short, the concrete block has to be removed. But it can’t be demolished with heavy machinery, because there’s too high a risk that doing so could damage the museum’s prize attraction, the Pergamon Altar, which dates to 2nd century Greece. Carefully demolishing the structure requires expensive specialized machinery, and takes time.

“The numbers we heard rose steadily over time,” Hermann Parzinger, president of the Prussian Cultural Heritage Foundation, which manages Berlin’s state museums, told Der Tagesspiegel. “In the end, it was really worrying. The fact that we are dealing with a complex building task was well known to all, but I didn’t foresee an increase of this magnitude in any way.”

Welcoming over 1 million visitors a year, the Pergamon Museum is one of Berlin’s top tourist destinations, according to the Art Newspaper. While parts of the museum are still accessible during the current work, the Pergamon Altar is not currently on view.