The “Thrown Stones”

On the way leading from Viterbo to Bolsena, following the road that borders the eastern coast of the lake bearing the same name, the landscape offers a great number of breathtaking visions of incredible beauty.


One of these is only a few kilometers before Bolsena and is characterized by a heap of stones which may go unnoticed tofast drivers. These stones, known as “The Thrown Stones” (“Pietre Lanciate” in Italian) have a story, a very ancient story, which is described in a panel and copied hereunder.

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“This stretch of Via Francigena crosses the Monti Volsini where unusual lava products are found: the so-called “Thrown Stones”, the strange shapes of which fired the imagination of many travellers on the road to Rome.

The morphology of these basaltic walls is the result processes that took place as the lava cooled and caused the formation of huge rocky prisms. The Vulsini area, covering the depression filled in by the Lake Bolsena and the calderas of Latera and Montefiascone, was formed by intense volcanic activity in this area that started one million years ago. At last one hundred individual cones or craters developed, with many eruptions through fissures, throughout the whole area. About five hundred thousand years ago, extremely violent explosions took place, projecting the material outside and thus emptying the subsoil; this caused an area of 270 sqkm to collapse into a caldera which was then filled by Lake Bolsena.

Towards the end of the period of volcanic activity, the islands Martana and Bisentina were formed as a result of explosions inside the lake. The lake is still in evolution and there are still some emanations of gas inside it: the last residues of the activity of the now extinct volcano. 

The popular name of “Thrown Stones”, commonly given to these particular rocks, was coined by the inhabitants in an attempt to understand what must certainly have been an inexplicable phenomenon.

In other words, they thought that the volcano that had been where the lake is now had thrown the stones up during an eruption and that they had stuck into the ground. The many, though slight. seismic shocks recorded in the area are a residue of the original volcanic activity to which this basaltic wall bears witness.” 

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