katty kay: segolene royal, of course, it will be lost on no christians around the world that yesterdayxt weekend is easter sunday, the holy week in the christian church. and as president macron has pointed out, catholics and christians in paris will be watching their beloved notre dame burn in this very holy, spiritual week. it's certainly for catholic and christians, it's all french people and all around the world. it's the most important monument in europe which is the most visited, and history belongs not only to christians. but i think that everybody is very sad tonight, whatever their origin. katty kay: ms royal, we heard earlierfrom ken follett who studied the construction of these buildings, that what can happen in a fire like this is that the roof collapses into the building. do you think that is why this blaze spread so quickly and so ferociously? it's a good explanation, you're right — it's a good explanation. the former french environment minister there. michael t davies is the chair of architectural studies at mount hollyoke college in massachusttes. this is certainly an oc