They knew it may happen. Three years ago an important report on Notre Dame was classified

PAP/EPA

Three years ago, specialists from the University of Versailles alarmed that there was a high risk of fire in the attic of Notre Dame. They warned that if the fire started, it would be impossible to save the roof and the spire, because there is no effective system to stop the spread of flames. However, the report was classified and its conclusions ignored by the French government.

The document was classified, because French authorities feared that making such information public would encourage terrorists to set fire to the cathedral.