Parisians and crowds looked on in horror as a massive fire broke out in the centuries old Notre Dame cathedral on Monday night.

As firefighters struggled for hours to put out the blaze, people gathered outside to mourn the damage to the beloved 850-year-old cathedral by singing hymns and prayers. In videos posted on social media, Parisians were seen singing Ave Maria and Hail Mary while some kneeled in prayer.

The fire caused the collapse of the cathedral’s spire and also ravaged one of its rectangular towers. But firefighters managed to stop the blaze before it spread to the main structure. The cause of the blaze was not immediately ascertained.