As fire ripped through France's iconic cathedral, stone vaults developed in the Middle Ages kept it from being destroyed beyond repair. //

According to architectural historians, the cathedral's medieval stone vaults — which served as a buffer for the fire after it burned through the wooden roof — had a hand in this.

Here's how an innovation developed in the 12th century held Notre Dame together, and what we can expect in terms of restoring the world's most famous Gothic cathedral of the Middle Ages.

Dr Robert Bork, an architectural historian at the University of Iowa, told the ABC the cathedral boasts some of the earliest six-part vaults used in the 12th century. //

Innovation and exploration in the Middle Ages resulted in the creation of wider vaults that would better allow for elaborate windows than previous Romanesque churches, he explained.

The general principle of a vault, Dr Bork explained, is the same as that behind an arch, which sees lots of stones that are relatively small work to span a large space.

"So, in Notre Dame, [these stones] cross the span which is about 14 metres across on the inside, and they're all essentially wedged together so that when gravity pulls down on each of those little stones, [the structure] is held into place by the friction of its neighbours in a kind of wedging action."

What this means, Dr Bork said, is that the complete arch or vault will weigh heavily down as well as pushing outwards, and this is where buttresses — which work to reinforce walls — come in to restrain the outward push.

Had Notre Dame not had these stone vaults, Dr Bork said it was "quite likely" we would be looking at an almost completely destroyed cathedral.

"The vaults are designed to be in dialogue with the buttressing system of the building … and if [Notre Dame] didn't have them, the buttresses would have just had brick walls and in cases where you just have a timber roof building and the roof burns off, frequently those walls will collapse."