The Cave of Dogs () is a cave near

Naples Naples ( ; ; ) is the Regions of Italy, regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 908,082 within the city's administrative limits as of 2025, while its Metropolitan City of N ...

, Italy. Volcanic gases seeping into the cave give the air inside a high concentration of

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

. Dogs held inside would faint; at one time this was a tourist attraction.

Description

The Cave of Dogs (, literally "Cave of the Dog")) is a

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

about ten metres deep on the eastern side of the

Phlegraean Fields The Phlegraean Fields (, ; ) is a large volcano, volcanic caldera west of Naples, Italy. The Neapolitan Yellow Tuff eruption (about 12ka BP) produced just 50 cubic kilometers. It is, however, one of relatively few volcanoes large enough to f ...

near

Pozzuoli Pozzuoli (; ; ) is a city and (municipality) of the Metropolitan City of Naples, in the Italian region of Campania. It is the main city of the Phlegrean Peninsula. History Antiquity Pozzuoli began as the Greek colony of ''Dicaearchia ...

. Inside the cave is a

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or another rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

that releases carbon dioxide of

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

origin. The cave is thought to have been constructed in classical antiquity, possibly as a

sudatorium In architecture, a sudatorium is a vaulted sweating-room ('' sudor'', "sweat") or steam bath (Latin: ''sudationes'', steam) of the Roman baths or thermae. The Roman architectural writer Vitruvius (v. 2) refers to it as ''concamerata sudatio''. It is ...

; if so, the CO emissions must have been much lower at the time. It may have been known to

Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...

, who, in his ''

Natural History Natural history is a domain of inquiry involving organisms, including animals, fungi, and plants, in their natural environment, leaning more towards observational than experimental methods of study. A person who studies natural history is cal ...

'' Chapter 95 (written 77–79 AD), mentions a location near

where animals die from poisonous fumes. However, the first unambiguous reports about the cave only appear in the 16th century. Later, it became a

tourist attraction A tourist attraction is a place of interest that tourists visit, typically for its inherent or exhibited natural or cultural value, historical significance, natural or built beauty, offering leisure and amusement. Types Places of natural beaut ...

for travelers on the Grand Tour. The CO gas, being denser than air, tended to accumulate in the deeper parts of the cave. As a result, small animals such as dogs held inside the cave suffered

carbon dioxide poisoning Hypercapnia (from the Greek ''hyper'', "above" or "too much" and ''kapnos'', "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous produ ...

, while a standing human was not affected. Local guides, for a fee, would suspend small animals (usually dogs) inside it until they became unconscious. The dogs could be revived by submerging them in the cold waters of the nearby

Lake Agnano __NOTOC__ Lago di Agnano or Lake Agnano was a circular lake, some 6½ km in circumference, which occupied the crater of the extinct volcano of Agnano 8 km west of Naples, Italy. It was apparently not formed until the Middle Ages, as it is not ...

, although in at least one case this led to the dog drowning instead. Tourists who came to see this attraction included Sir

Thomas Browne Sir Thomas Browne ( "brown"; 19 October 160519 October 1682) was an English polymath and author of varied works which reveal his wide learning in diverse fields including science and medicine, religion and the esoteric. His writings display a d ...

Richard Mead Richard Mead, FRSFRCP (11 August 1673 – 16 February 1754) was an English physician. His work, ''A Short Discourse concerning Pestilential Contagion, and the Method to be used to prevent it'' (1720), was of historic importance in advancing t ...

Goethe Johann Wolfgang (von) Goethe (28 August 1749 – 22 March 1832) was a German polymath who is widely regarded as the most influential writer in the German language. His work has had a wide-ranging influence on Western literature, literary, Polit ...

John Evelyn John Evelyn (31 October 162027 February 1706) was an English writer, landowner, gardener, courtier and minor government official, who is now best known as a diary, diarist. He was a founding Fellow of the Royal Society. John Evelyn's Diary, ...

Montesquieu Charles Louis de Secondat, baron de La Brède et de Montesquieu (18 January 168910 February 1755), generally referred to as simply Montesquieu, was a French judge, man of letters, historian, and political philosopher. He is the principal so ...

Alexandre Dumas père Alexandre Dumas (born Alexandre Dumas Davy de la Pailleterie, 24 July 1802 – 5 December 1870), also known as Alexandre Dumas , was a French novelist and playwright. His works have been translated into many languages and he is one of the mos ...

, and

Mark Twain Samuel Langhorne Clemens (November 30, 1835 – April 21, 1910), known by the pen name Mark Twain, was an American writer, humorist, and essayist. He was praised as the "greatest humorist the United States has produced," with William Fau ...

. Dutch traveller

Cornelis de Bruijn Cornelis de Bruijn or Cornelius de Bruyn (; 16521726/7), also formerly known in English by his French name Corneille Le Brun, was a Dutch artist and traveler. He made two large tours and published illustrated books with his observations of peop ...

also reported visiting the caves in the year 1677. He wrote:

Next, one comes close to the road by a small cave called Grotta del Cani, which is very venomous, to the extent that if a dog is kept inside, it dies very quickly. I had the curiosity to visit it with two different dogs and found that when the animal remains standing on its legs, it is not harmed by the poison. However, if one forcibly presses it down, it quickly loses its strength after great struggling and desperate resistance, and would undoubtedly die in an instant if not promptly picked up and thrown into a nearby water or lake, where it immediately recovers but with some dizziness, walking like a human who is completely drunk. This lake has the same nature as the cave and boils in several places due to the great heat of sulfur. Curiosity drove me to investigate how high the venom in the cave might be from the ground, so bowing my head downward, I found it to be only one foot high from the ground.

Some tourists including

Washington Irving Washington Irving (April 3, 1783 – November 28, 1859) was an American short-story writer, essayist, biographer, historian, and diplomat of the early 19th century. He wrote the short stories "Rip Van Winkle" (1819) and "The Legend of Sleepy ...

(1804), Percy Bysshe and

Mary Shelley Mary Wollstonecraft Shelley ( , ; ; 30 August 1797 – 1 February 1851) was an English novelist who wrote the Gothic novel ''Frankenstein, Frankenstein; or, The Modern Prometheus'' (1818), which is considered an History of science fiction# ...

(1818) and

Ralph Waldo Emerson Ralph Waldo Emerson (May 25, 1803April 27, 1882), who went by his middle name Waldo, was an American essayist, lecturer, philosopher, minister, abolitionism, abolitionist, and poet who led the Transcendentalism, Transcendentalist movement of th ...

(1833), objecting to the cruelty, refused to pay for the experiment to be performed on the dog. A Scottish scientist who examined the cave for several days (1877) reported: The lake became polluted, was thought to be malarious, and was drained in 1870. At some point the spectacle fell into disuse, although

Baedeker Verlag Karl Baedeker, founded by Karl Baedeker on 1 July 1827, is a German publisher and pioneer in the business of worldwide travel guides. The guides, often referred to simply as "List of Baedeker Guides, Baedekers" (a term sometimes used to re ...

's guides in the 1880s were still advertising that to see the dog experiment would cost tourists 1 ''lire'' (≈ 20 U.S. cents). According to one source, it was banned before World War II for cruelty to animals. The cave entrance was blocked to prevent access by children. In 2001 the cave was investigated by Italian

speleologists Speleology () is the scientific study of caves and other karst features, as well as their composition, structure, physical properties, history, ecology, and the processes by which they form (speleogenesis) and change over time (speleomorpholog ...

. Nine metres from its entrance the temperature was and the CO concentration was 80%, with negligible oxygen.

In popular science

The cave was often described in nineteenth century science textbooks to illustrate the

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

and toxicity of carbon dioxide,The above image is from L'air et le monde aèrien, an 1865 textbook by Arthur Mangin, p.16

/ref> and its reputation gave rise to a

scientific demonstration A scientific demonstration is a procedure carried out for the purposes of demonstrating scientific principles, rather than for hypothesis testing or knowledge gathering (although they may originally have been carried out for these purposes). Mos ...

of the same name, in which stepped candles are successively extinguished by tipping carbon dioxide into a transparent container.

References

{{Coord, 40.833333, N, 14.166667, E, display=title

External links

Video of a scientific demonstration of the principle behind Cave of Dogs

Report from a scientific expedition to the cave on April 28, 2013
(in Italian) Caves of Italy Carbon dioxide Campanian volcanic arc Cruelty to animals Science demonstrations Toxicology Tourist attractions in Campania Volcanism of Italy Geotourism Phlegraean Fields