 Over the centuries , the cathedral has suffered damage . A fire in 1967 destroyed a significant part of the cathedral 's interior . The restoration work that followed uncovered a number of important documents and artwork that had previously been hidden . Although a solid foundation was built for the cathedral , the soft clay soil it is built on has been a threat to its structural integrity . Dropping water tables and accelerated sinking caused the structure to be added to the World Monuments Fund list of the 100 Most Endangered Sites . Reconstruction work beginning in the 1990s stabilized the cathedral and it was removed from the endangered list in 2000 . 
 Over the centuries , the cathedral <a href='been_done' title='1'><mark>has</mark></a> suffered damage . A fire in 1967 destroyed a significant part of the cathedral <a href='null_genetive' title='2'><mark>'s</mark></a>interior . The restoration work <a href='null_relcl' title='3'><mark>that</mark></a>followed uncovered a number of important documents and artwork <a href='null_relcl' title='4'><mark>that</mark></a><a href='been_done' title='5'><mark>had</mark></a> previously been hidden . Although a solid foundation was built for the cathedral , the soft clay soil it is built on <a href='uninflect' title='6'><mark>has</mark></a> been a threat to its structural integrity . Dropping water tables and accelerated sinking caused the structure to be added to the World Monuments Fund list of the 100 Most Endangered Sites . Reconstruction work beginning in the 1990s stabilized the cathedral and it was removed from the endangered list in 2000 . 
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