In medieval times, the humble "house-leek" or "Jupiter's beard", as it was known colloquially, was believed to ward off lightning when grown on the rooftop of a house or church. So efficacious was it in this respect, indeed, that it received from the Holy Roman Emperor an imprimatur:Habet quisque supra domum suum Jovis barbam, ordered Charlemagne - "Let each one have above his house the beard of Jupiter."
But in the case of churches, it was not infallible. Because of their great height, providing with their spires usually the highest point in the locality, churches were particularly vulnerable to fire from lightning. Fulgura Frango, "I break up lightning flashes," is a motto found inscribed on many church bells surviving from those times, and it recalls the practice of supplementing the power of prayer to ward off lightning strikes by the violent ringing of the bells.
The poor believed that this pious exercise dispersed the evil spirits of the storm. The more sophisticated were of the view that the peal of the bells caused some kind of undulation of the air, which broke the continuity of the lightning path. In any event, the practice of ringing church bells in thunderstorms was an extremely dangerous one for the bell-ringers, and following a great number of fatalities the practice was banned by the more enlightened rulers of the day.
But the problem, nonetheless, remained. In fact it is rare to find a cathedral or church of any age in Europe that has not experienced at some stage in its life a fire caused by lightning. The Basilica of Saint-Denis, just north of Paris, for example, is the burial place of almost all the kings of France, and looks incomplete with its single asymmetric tower. And so it is: the north tower, it seems, was damaged by a lightning-fire in 1859 and had to be demolished.
And on the coast of Normandy, the Abbey Church of Mont St Michel had a similar experience in the previous century: apparently its "new", and some would say incongruous, Georgian facade was added after its twin-towered predecessor in the Romanesque style proved unequal to a thunderstorm in 1776.
Even with lightning conductors, the problem continues in our time. Just five years ago this month, in July 1994, a rash of lightning fires occurred in south Wales and included a major conflagration at an oil refinery in Milford Haven. And it was exactly 15 years ago today, July 9th, 1984, that York Minster, the primatial seat of the archbishop of that city, was almost completely destroyed by a fire that was started by a stroke of lightning.