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The miscommunication, uncovered in interviews with church officials and managers of the fire security company, Elytis, has set off a bitter round of finger-pointing over who was responsible for allowing the fire to rage unchecked for so long. Who is to blame and how the fire started have not yet been determined and are at the heart of an investigation by the French authorities that will continue for months.

But the damage is done. What happened that night changed Paris. The cathedral — a soaring medieval structure that has captured the hearts of believer and nonbeliever alike for 850 years — was ravaged.

Today three jagged openings mar Notre-Dame’s vaulted ceiling, the stone of the structure is precarious, and the roof is gone. Some 150 workers remain busy recovering the stones, shoring up the building, and protecting it from the elements with two giant tarps.

Some of what went wrong that night has been reported in the French news media, including Le Monde and Le Canard Enchaîné. Now, The New York Times conducted scores of interviews and reviewed hundreds of documents to reconstruct the missteps — and the battle that saved Notre-Dame in the first four critical hours after the blaze began.

What became clear is just how close the cathedral came to collapsing.

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