Subterranean Paris

Underground Paris resembles a Swiss cheese with hundreds of kilometers of tunnels built during Roman times lying far below the elegant Parisian boulevards and metro.

However, only a small section is actually accessible to the general public.

That is, apart from a faceless, covert, underworld group of people, known as "Cataphiles". They enter the vast network of tunnels that criss cross the city illegally by way of secret entrances. It is estimated that at least 300 Cataphiles visit this dark labyrinth every week crawling along the narrow, low passageways, dropping down or climbing up through small holes to different levels, and often encountering unexpected obstacles and hazards such as rock falls, flooding, and large pools of water. I can only assume that the dangers experienced in this dark, mysterious, unmapped, underground world excites them and is accompanied by an extreme adrenaline rush. 

The descent for the paying public is via a stone spiral stairway of 130 steps; including exploring the passages the whole visit lasts approximately one hour. I should say that it is not a good idea to go if you have any anxieties about being underground or find descending or ascending steps for a long distance difficult.

Between street level and the area where the Catacombs are located, the visitor travels back in geological time for nearly 45 million years. Descending through a succession of rock layers before reaching a limestone bank from the Lutetian period. The Roman name for Paris was Lutetia, and the limestone cut from that stage provides very high quality cut stone commonly referred to as "pierre de Paris" - Parisian stone. Notre Dame, The Louvre, and  most of Paris's principal buildings were built from this stone.

 This shell was more than one metre in length

Entrance to the Catacombs - "Stop, this is death's empire!"
 Thus begins the pathway that leads through the remains of more than six million Parisians.  

Overflowing cemeteries were a huge problem for 18th century Paris. Those living in the neighbourhood of Les Halles near Les Innocents, the city's oldest and largest cemetery, were amongst the first to complain. They reported that the cemetery exuded a strong smell of decomposing flesh. 
In 1763, Louis XV issued an edict banning all burials from occurring inside the capital. At that time the church was very powerful and chose to ignore the ruling as it did not want it's cemeteries disturbed or moved. However, in 1780 a prolonged period of spring rains caused walls around Les Innocents to collapse, spilling rotting corpses into the surrounding neighbourhood, this episode finally resulted in the removal of millions of bones from various city cemeteries into the quarry. The task took 12 years to complete with some of the oldest bones dating back more than 1,200 years.

The Inspector General of the Quarries, Héricart de Thury was responsible for developing the Ossuary. The long bones and skulls were arranged decoratively to form a back wall behind which other bones were piled. He also created signage indicating from which Parisian cemetery the bones originated.

The Catacombs became a great curiosity for the more privileged Parisians - the first known visitor of note was the Count of Artois, later France's King Charles X. 

 via

Public visits began during the beginning of the early 19th century but infrequently. As a result of the wave of increasing curiosity that attracted a growing number of visitors the government decided to allow monthly visits. Today the Catacombs are open every day apart from Mondays and some Public holidays throughout the year.

Crypt of the Passion: The Barrel

At midnight on the 2nd April 1897, a two hour clandestine concert was held around The Barrel attended by 100 members of Parisian "high society"  which featured Chopin's Funeral March, La Danse Macabre by Camille Saint-Saëns, and Marche Funèbre from Beethoven's Eroica.