In the first episode of Civilisation (1969), “The Skin of our Teeth,” Kenneth Clark takes on why the Roman Empire fell:

“However complex and solid it seems, civilisation is actually quite fragile. It can be destroyed. What are its enemies? Well, first of all fear — fear of war, fear of invasion, fear of plague… fears that make it simply not worthwhile constructing things, or planting trees or even planning next year’s crops. And fear of the supernatural, which means that you daren’t question an...