Grand Tour

Among the curiosities of nature which caught travelers’ imagination were «the burning mountains», as Mary Montagu called them, a phenomenon which was viewed as something very rare by all naturalists. Lady Montagu spoke of a cavity, of unknown depth, from which sprang a smokeless flame that had no effect on the surrounding land, well cultivated and at a perfectly normal temperature. The peculiarity lay in the fact that, when the ground was scraped, «a flame comes out which does not burn and does not last as long as that of volcanoes.» De Brosses (1740) also stopped at Pietramala, where the rocks «absorb the light of the sun and form a sort of phosphorus, » and, on seeing them, took Misson (1688) to task for having exaggerated in his claim that the rocks gave off a flame like that of a bonfire. Who knows what he would have had to say about Delpuech de Comeiras (1804), who asserted that Pietramala was famous for its «volcano»!

The reason why observers (Young, Wright, Gray and Chetwode Eustace, among others) offered such different explanations can be sought in the fact that the sources of the fire were in reality located in three different places, and the phenomena were not all of the same kind. The spot described by Lady Montagu was probably the one called Acqua Buia (“Dark Water”). At that point the outlet of the fire had formed a small pool of water that boiled with the gas emerging from beneath the ground. This almost always put out the fire, except when the pool dried up. A. C. Valéry too spoke of «dark water» (1828). Mary Montagu’s comparison with volcanoes was not so far-fetched. Many people believed the burning lands actually to be the mouth of a volcano, with the result that, as Targioni Tozzetti noted, gold coins, idols and amulets were found in this area, in all likelihood left there as propitiatory gifts.

The fires of Pietramala have now vanished, but before going out they prompted many travelers to make conjectures about their origin. Alessandro Volta, who made a close study of them in 1780, was the first to give a scientific explanation of their existence: the ground was steeped in methane (which has now been extracted), emitted naturally by small deposits of oil. Escaping from cracks in the clayey ground, it caught fire when struck by lightning.

Such grand natural phenomena were not the only ones that caught the attention of travelers. Depending on their sensitivity and spirit of observation, apparently insignificant things could become the subject of comment or poetry in their accounts. This is how M.me du Boccage recalled her encounter with a swarm of fireflies at night, in the gardens of Palazzo Pitti: «a phenomenon, new for me, distracted me. A swarm of phosphorescent fireflies hovered in the garden. I mistook it for a mobile illumination. When I approached, the lamps fled. I had never met more than two or three of these luminous insects at a time. Their multitude fascinated and surprised me; parva leves capiunt animos».