Ancient corridors below the French capital have served as its ossuary, playground, brewery, and perhaps soon, air conditioning.
- People have been digging up limestone and gypsum from below Paris since Roman times.
- They left behind a vast network of corridors and galleries, since reused for many purposes — most famously, the Catacombs.
- Soon, the ancient labyrinth may find a new lease of life, providing a sustainable form of air conditioning.
Ancient mining areas below Paris for limestone (red) and gypsum (green).Credit: Émile Gérards (1859–1920) / Public domain
"If you're brave enough to try, you might be able to catch a train from UnLondon to Parisn't, or No York, or Helsunki, or Lost Angeles, or Sans Francisco, or Hong Gone, or Romeless."
China Miéville's fantasy novel Un Lun Dun is set in an eerie mirror version of London. In it, he hints that other cities have similar doubles. On the list that he offhandedly rattles off, Paris stands out. Because the City of Light really does have a twisted sister. Below Paris Overground is Paris Underground, the City of Darkness.
Most people will have heard of the Catacombs of Paris: subterranean charnel houses for the bones of around six million dead Parisians. They are one of the French capital's most famous tourist attractions – and undoubtedly its grisliest.
But they constitute only a small fragment of what the locals themselves call les carrières de Paris ("the mines of Paris"), a collection of tunnels and galleries up to 300 km (185 miles) long, most of which are off-limits to the public, yet eagerly explored by so-called cataphiles.
The Grand Réseau Sud ("Great Southern Network") takes up around 200 km beneath the 5th, 6th, 14th, and 15th arrondissements (administrative districts), all south of the river Seine. Smaller networks run beneath the 12th, 13th, and 16th arrondissements. How did they get there?
Paris stone and plaster of Paris
It all starts with geology. Sediments left behind by ancient seas created large deposits of limestone in the south of the city, mostly south of the Seine; and gypsum in the north, particularly in the hills of Montmartre and Ménilmontant. Highly sought after as building materials, both have been mined since Roman times.
The limestone is also known as Lutetian limestone (Lutetia is the Latin name for ancient Paris) or simply "Paris stone." It has been used for many famous Paris landmarks, including the Louvre and the grand buildings erected during Georges-Eugène Haussmann's large-scale remodelling of the city in the mid-19th century. The stone's warm, yellowish color provides visual unity and a bright elegance to the city.
The fine-powdered gypsum of northern Paris, used for making quick-setting plaster, was so famed for its quality that "plaster of Paris" is still used as a term of distinction. However, as gypsum is very soluble in water, the underground cavities left by its extraction were extremely vulnerable to collapse.
Like living on top of a rotting tooth: subsidence starts far below the surface, but it can destroy your house.Credit : Delavanne Avocats
In previous centuries, a road would occasionally open up to swallow a chariot, or even a whole house would disappear down a sinkhole. In 1778, a catastrophic subsidence in Ménilmontant killed seven. That's why the Montmartre gypsum quarries were dynamited rather than just left as they were. The remaining gypsum caves were to be filled up with concrete.
The official body governing Paris down below is the Inspection Générale des Carrières (IGC), founded in the late 1770s by King Louis XVI. The IGC was tasked with mapping and, where needed, propping up the current and ancient (and sometimes forgotten) mining corridors and galleries hiding beneath Paris.
A delightful hiding place
Also around that time, the dead of Paris were getting in the way of the living. At the end of the 18th century, their final destination consisted of about 200 small cemeteries, scattered throughout the city — all bursting at the seams, so to speak. There was no room to bury the newly dead, and the previously departed were fouling up both the water and air around their respective churchyards.
Something radical had to happen. And it did. From 1785 until 1814, the smaller cemeteries were emptied of their bones, which were transported with full funerary pomp to their final resting place in the ancient limestone quarries at Tombe-Issoire. Three large and modern cemeteries were opened to receive the remains of subsequent generations of Parisians: Montparnasse, Père-Lachaise, and Passy.
The six million dead Parisians in the Catacombs, from all corners of the capital and across many centuries, together form the world's largest necropolis — their now anonymized skulls and bones methodically stacked, occasionally into whimsical patterns. The Catacombs are fashioned into a memorial to the brevity of life. The message above the entrance reads: Arrête! C'est ici l'empire de la Mort. ("Halt! This is the empire of Death.")
That has not stopped the Catacombs, accessible via a side door to a classicist building on the Avenue du Colonel Henri Rol-Tanguy, making just about every Top 20 list of things to see in Paris.
An underground economy
However, while the Catacombs certainly are the most famous part of the centuries-old network beneath Paris, and in non-pandemic times draw thousands of tourists each day, they constitute just 1.7 km (1 mile) of the 300-km (185-mile) tunneling total.
Subterranean Paris wasn't just used for mining and storing dead people. In the 17th century, Carthusian monks converted the ancient quarries under their monastery into distilleries for the green or yellow liqueur that still carries their name, chartreuse.
Because the mines generally keep a constant cool temperature of around 15° C (60° F), they were also ideal for brewing beer, as happened on a large scale from the end of the 17th century until well into the 20th century. Several caves were dug especially for establishing breweries, and not just because of the ambient temperature: going underground allowed brewers to remain close to their customers without having to pay a premium for real estate up top.
Overview of the Paris Catacombs.Credit: Inspection Générale des Carrières, 1857 / Public domain.
At the end of the 19th century, the underground breweries of the 14th arrondissement alone produced more than a million hectoliters (22 million gallons) per year. One of the most famous of Paris' underground breweries, Dumesnil, stayed in operation until the late 1960s.
In that decade, the network of corridors and galleries south of the Seine, long since abandoned by miners, became the unofficial playground for the young people of Paris. They explored the fantastical world beneath their feet, in some cases via entry points located in their very schools. Fascinated, these cataphiles ("catacomb lovers") read up on old books, explored the subterranean labyrinth, and drew up schematics that were passed around among fellow initiates as reverently as treasure maps.
As Robert Macfarlane writes in Underland, Paris-beneath-their-feet became "a place where people might slip into different identities, assume new ways of being and relating, become fluid and wild in ways that are constrained on the surface."
Some larger caves turned into notorious party zones: a 7-meter-tall gallery below the Val-de-Grâce hospital is widely known as "Salle Z." Over the last few decades, various other locations in subterranean Paris have hosted jazz and rock concerts and rave parties — like no other city, Paris really has an "underground music scene."
Hokusai's Great Wave as the backdrop to the "beach" under Paris.Credit: Reddit
Cataphiles vs. cataphobes
With popularity came increased reports of nuisance and crime — the tunnels provided easy access to telephone cables, which were stolen for the resale value of their copper.
The general public's "discovery" of the underground network led the city of Paris to officially interdict all access by non-authorized persons. That decree dates back to 1955, but the "underground police" have an understanding with seasoned cataphiles. Their main targets are so-called tourists, who by their lack of knowledge expose themselves to risk of injuries or worse, and degrade their surroundings, often leaving loads of litter in their wake.
The understanding does not extend to the IGC. Unlike in the 19th century, when weak cavities were shored up by purpose-built pillars, the policy now is to inject concrete to fill up endangered spaces — thus progressively blocking off parts of the network. That procedure has also been used to separate the Catacombs to prevent "infiltration" of the site by cataphiles.
Many subterranean streets have their own names, signs and all. This is the Rue des Bourguignons (Street of the Burgundians) below the Champs des Capucins (Capuchin Field), neither of which exists on the surface.Credit: Jean-François Gornet via Wikimedia and licensed under
The cataphiles, however, are fighting back. In a game of cat and mouse with the authorities, they are reopening blocked passages and creating chatières ("cat flaps") through which they can squeeze into chambers no longer accessible via other underground corridors.
Catacomb climate control
Alone against the unstoppable tide of concrete, the amateurs of Underground Paris would be helpless. But the fight against climate change may turn the subterranean labyrinths from a liability into an asset — and the City of Paris into an ally.
The UN's 2015 Climate Plan — concluded in Paris, by the way — requires the world to reduce greenhouse gas emissions by 75 percent by 2050. And Paris itself wants to be Europe's greenest city by 2030. More sustainable climate control of our living spaces would be a great help toward both targets. A lot of energy is spent heating houses in winter and cooling them in summer.
This is where the constant temperature of the Parisian tunnels comes in. It's not just good for brewing beer; it's a source of geothermal energy, says Fieldwork, an architectural firm based in Paris. It can be used to temper temperatures, helping to cool houses in summer and warming them in winter.
One catch for the cataphiles: it also works when the underground cavities are filled up with concrete. So perhaps one day, Paris Underground, fully filled up with concrete, will completely fall off the map, reducing the city's formerly real doppelgänger into an air conditioning unit.
Cool in summer, warm in winter: Paris Underground could become Paris A/C.Credit: Fieldwork
Strange Maps #1083
Got a strange map? Let me know at firstname.lastname@example.org.
According to international law, the seabed belongs to everyone.
Mining the ocean floor for submerged minerals is a little-known, experimental industry.
But soon it will take place on the deep seabed, which belongs to everyone, according to international law.
Seabed mining for valuable materials like copper, zinc and lithium already takes place within countries' marine territories. As soon as 2025, larger projects could start in international waters – areas more than 200 nautical miles from shore, beyond national jurisdictions.
We study ocean policy, marine resource management, international ocean governance and environmental regimes, and are researching political processes that govern deep seabed mining. Our main interests are the environmental impacts of seabed mining, ways of sharing marine resources equitably and the use of tools like marine protected areas to protect rare, vulnerable and fragile species and ecosystems.
Today countries are working together on rules for seabed mining. In our opinion, there is still time to develop a framework that will enable nations to share resources and prevent permanent damage to the deep sea. But that will happen only if countries are willing to cooperate and make sacrifices for the greater good.
An old treaty with a new purpose
Countries regulate seabed mining within their marine territories. Farther out, in areas beyond national jurisdiction, they cooperate through the Law of the Sea Convention, which has been ratified by 167 countries and the European Union, but not the U.S.
The treaty created the International Seabed Authority, headquartered in Jamaica, to manage seabed mining in international waters. This organization's workload is about to balloon.
Under the treaty, activities conducted in areas beyond national jurisdiction must be for "the benefit of mankind as a whole." These benefits could include economic profit, scientific research findings, specialized technology and recovery of historical objects. The convention calls on governments to share them fairly, with special attention to developing countries' interests and needs.
The United States was involved in negotiating the convention and signed it but has not ratified it, due to concerns that it puts too many limits on exploitation of deep sea resources. As a result, the U.S. is not bound by the treaty, although it follows most of its rules independently. Recent administrations, including those of Presidents Bill Clinton, George W. Bush and Barack Obama, sought to ratify the treaty, but failed to muster a two-thirds majority in the Senate to support it.Locations of three main types of marine mineral deposits: polymetallic nodules (blue); polymetallic or seafloor massive sulfides (orange); and cobalt-rich ferromanganese crusts (yellow). Miller et al., 2018, https://doi.org/10.3389/fmars.2017.00418, CC BY
Powering digital devices
Scientists and industry leaders have known that there are valuable minerals on the seafloor for over a century, but it hasn't been technologically or economically feasible to go after them until the past decade. Widespread growth of battery-driven technologies such as smartphones, computers, wind turbines and solar panels is changing this calculation as the world runs low on land-based deposits of copper, nickel, aluminum, manganese, zinc, lithium and cobalt.
These minerals are found in potato-shaped "nodules" on the seafloor, as well as in and around hydrothermal vents, seamounts and midocean ridges. Energy companies and their governments are also interested in extracting methane hydrates – frozen deposits of natural gas on the seafloor.
Scientists still have a lot to learn about these habitats and the species that live there. Research expeditions are continually discovering new species in deep-sea habitats.
Korea and China seek the most contracts
Mining the deep ocean requires permission from the International Seabed Authority. Exploration contracts provide the right to explore a specific part of the seabed for 15 years. As of mid-2020, 30 mining groups have signed exploration contracts, including governments, public-private partnerships, international consortiums and private multinational companies.
Two entities hold the most exploration contracts (three each): the government of Korea and the China Ocean Mineral Resources R&D Association, a state-owned company. Since the U.S. is not a member of the Law of the Sea treaty, it cannot apply for contracts. But U.S. companies are investing in others' projects. For example, the American defense company Lockheed Martin owns UK Seabed Resources, which holds two exploration contracts.
Once an exploration contract expires, as several have since 2015, mining companies must broker an exploitation contract with the International Seabed Authority to allow for commercial-scale extraction. The agency is working on rules for mining, which will shape individual contracts.
Unknown ecological impacts
Deep-sea mining technology is still in development but will probably include vacuuming nodules from the seafloor. Scraping and vacuuming the seafloor can destroy habitats and release plumes of sediment that blanket or choke filter-feeding species on the seafloor and fish swimming in the water column.
Mining also introduces noise, vibration and light pollution in a zone that normally is silent, still and dark. And depending on the type of mining taking place, it could lead to chemical leaks and spills.
Many deep-sea species are unique and found nowhere else. We agree with the scientific community and environmental advocates that it is critically important to analyze the potential effects of seabed mining thoroughly. Studies also should inform decision-makers about how to manage the process.
This is a key moment for the International Seabed Authority. It is currently writing the rules for environmental protection but doesn't have enough information about the deep ocean and the impacts of mining. Today the agency relies on seabed mining companies to report on and monitor themselves, and on academic researchers to provide baseline ecosystem data.
We believe that national governments acting through the International Seabed Authority should require more scientific research and monitoring, and better support the agency's efforts to analyze and act on that information. Such action would make it possible to slow the process down and make better decisions about when, where and how to mine the deep seabed.
Balancing risks and benefits
The race for deep-sea minerals is imminent. There are compelling arguments for mining the seabed, such as supporting the transition to renewable energy, which some companies assert will be a net gain for the environment. But balancing benefits and impacts will require proactive and thorough study before the industry takes off.
We also believe that the U.S. should ratify the Law of the Sea treaty so that it can help to lead on this issue. The oceans provide humans with food and oxygen and regulate Earth's climate. Choices being made now could affect them far into the future in ways that aren't yet understood.
Dr. Rachel Tiller, Senior Research Scientist with SINTEF Ocean, Norway, contributed to this article.
Elizabeth M. De Santo, Associate Professor of Environmental Studies, Franklin & Marshall College; Elizabeth Mendenhall, Assistant Professor of Marine Affairs and Political Science, University of Rhode Island, and Elizabeth Nyman, Assistant Professor of Maritime Policy, Texas A&M University
A European start-up uses satellite data to pinpoint individual sources of abnormal methane concentration.
- Just 100 sources of methane emit 20 megatons each year.
- Thanks to satellite data, individual culprits can now be found.
- The new tech could be used to police 'abnormal' methane emissions.
Significant contributor to global warming
Nodding donkey in Midland, Texas. The oil and gas industry is a major emitter of methane.
Image: Eric Kounce TexasRaiser, public domain
Methane is the second most important greenhouse gas (after CO2), and its concentration in the atmosphere is increasing at around 1% each year. Because it absorbs the sun's heat even more efficiently than CO2, it's a significant contributor to global warming.
The first step to fight the rise in methane emissions is to track who's doing it. That's just become a lot easier. Paris-based tech start-up Kayrros can now find individual sources of abnormal methane emissions, all across the world. That's a first, and it's made possible by data from the Copernicus Sentinel-5P satellite.
Developed by the European Space Agency (ESA) and launched in 2017, the British-built Sentinel-5 Precursor (Sentinel-5P) is the first satellite of the Copernicus program dedicated to monitoring air pollution, thanks to a spectrometer called Tropomi (short for Tropospheric Monitoring Instrument).
With a resolution of about 50 km2, this Dutch-built instrument can monitor atmospheric levels of aerosols, sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), formaldehyde (CH2O), ozone (O3) and methane (CH4).
High-volume methane leaks
Abnormal methane concentrations in 2019 – often found in regions of the world producing or processing oil and gas. Data provided by the Copernicus program, processed by Kayrros.
You may not have heard of Tropomi yet, but it's likely you've already seen its work. Earlier this year, Copernicus Sentinel-5P produced the images that showed substantially reduced NO2 levels across China, due to the coronavirus lockdown.
Tropomi also offers the most detailed monitoring of methane emissions presently available. Combining that data with other input from older-model Copernicus satellites Sentinel-1 and Sentinel-2, and from other sources (including ground sensors, position tracking and even social media), Kayrros scientists can identify the size, potency, and location of abnormal methane leaks around the world.
According to Kayrros, there are around 100 high-volume methane leaks active around the world at any given time. Together, they release about 20 megatons of methane per year. About half of that volume is associated with mining for oil, gas or coal, or other heavy industries. Together, that amount of methane per annum is equivalent to CO2 emissions of France and Germany combined.
So, how precise is the Kayrros method? Here's a recent case study.
Plume over the Permian Basin
In December last year, Kayrros used data from Copernicus-5P to identify the source of a methane plume over the Permian Basin, which covers western Texas and southeastern New Mexico. Sitting on top of a part of the Mid-Continent Oil Field, the Basin's surface is dotted with hundreds of oil wells. Yet with a little help from Sentinel-1 and Sentinel-2, Copernicus-5P managed to find the exact location, and the individual culprit.
For the first time, Kayrros tech and Copernicus-5P data make it possible to detect abnormal methane emissions in real time. Not only will this increase the precision of methane emission estimates, it will also allow regulators to find and fine the exact culprits, and if necessary, shut down their operations.
Found: the culprit
Strange Maps #1027
Got a strange map? Let me know at email@example.com.
The private sector may need the Outer Space Treaty to be updated before it can make any claims to celestial bodies or their resources.
- The Outer Space Treaty, which was signed in 1967, is the basis of international space law. Its regulations set out what nations can and cannot do, in terms of colonization and enterprise in space.
- One major stipulation of the treaty is that no nation can individually claim or colonize any part of the universe—when the US planted a flag on the Moon in 1969, it took great pains to ensure the world it was symbolic, not an act of claiming territory.
- Essentially to do anything in space, as a private enterprise, you have to be able to make money. When it comes to asteroid mining, for instance, it would be "astronomically" expensive to set up such an industry. The only way to get around this would be if the resources being extracted were so rare you could sell them for a fortune on Earth.
Could 16 Psyche make every person on Earth a billionaire? The space mining race is heating up.
- 16 Psyche is an asteroid full of metal in the asteroid belt that could be worth $700 quintillion.
- NASA plans to visit 16 Psyche by 2026.
- Commercial mining of faraway asteroids could still be decades away and some set closer targets, like the moon.
Would you like to be a billionaire? All you have to do is figure out how to go into space and mine 16 Psyche, an asteroid made of gold and other metals like iron and nickel. Flying somewhere between Mars and Jupiter, this amazing space rock is estimated to be worth as much as $700 quintillion, thanks to all the metals it contains.
Quintillion, if you are wondering, is 1 with 18 zeroes. It's such a large amount of money that if you divide it up between everyone alive on Earth currently, each person would get about $93 billion.
Of course, don't pack your bags for your new palace just yet – the prospect of actually getting such a giant chunk of precious metals back to Earth is difficult and hasn't been accomplished yet even on much smaller scales. And 16 Psyche is a truly massive space rock at over 200 km (120 mi) in diameter. It is one of the largest asteroids flying in the asteroid belt.
Experts, like Professor Zarnecki of the Royal Astronomical Society, conjecture we may be up to 50 years away from being able to carry out commercial mining operations of that size. To start things off, NASA is planning to send a Discovery Mission to the asteroid in 2022, which will arrive there by 2026.
Some skeptics also don't believe the asteroid is as full of expensive things as we think, with Peter Schiff of Euro Pacific Capital tweeting that 16 Psyche may just be "made almost entirely of an iron-nickel alloy, with small amounts of other metals, likely to include gold." He thinks the news about the asteroid are just out there to help bitcoin, which would benefit from the price of gold going down.
There are also other questions to consider – if it really is so full of gold and other riches, the asteroid could actually crash Earth's economy, which at $75.5 trillion is a pittance against the amount of money one could get from the asteroid.
Artist's conceptual drawing of the Psyche spacecraft, which will be used to directly explore 16 Psyche.
Veteran miner Scott Moore, CEO of the mining company EuroSun Mining, explained to Oil Price that: "The 'Titans of Gold' now control hundreds of the best-producing properties around the world, but the 4-5 million ounces of gold they bring to the market every year pales in comparison to the conquests available in space."
Of course, the thinking that a space gold rush that discovers a vast amount of heavy metals could bring down Earth's affairs is based on the current state of economy and the needs of the present day. Decades from now our requirements for metal might be entirely different.
16 Psyche was actually discovered back in 1852 by the Italian astronomer Annibale de Gasparis, and named after the Greek mythological character Psyche.
Besides this giant rock in the asteroid belt, there are other mining opportunities much closer to Earth. Moore points out that while Psyche "may be the Holy Grail of space exploration for gold," near-Earth asteroids are much better first targets for mining. Even our moon might be a better place to start such operations. It also has gold as well as platinum and other rare earth metals.
In other nearer goals, Deep Space Industries and Planetary Resources each plan to mine the 2011 UW158 asteroid, worth up to $5.7 trillion.
Lest you think this is all science fiction, Morgan Stanley projects the global space economy to be already worth $350 billion, which it thinks will grow to trillions by 2040. The race is on between the U.S., China, Japan and even small Luxembourg, which has 10 space-mining companies registered.