Quarries and subsoil of Paris’s 18th arrondissement
Moderate risk Paris 75018
The 18th arrondissement (Montmartre, Goutte-d’Or, Clignancourt) was mined for gypsum (plaster) from the Middle Ages onwards. Gypsum, which is soluble in water, presents a risk of dissolution and sinkholes (fontis), aggravated by underground water circulation. Several events have marked the sector: the Montmartre « earthquake » of 1843 (underground collapse), the collapses in rues Audran and Constance in 1993, and the gaping hole in rue des Martyrs in 2001.
What the public data say about the 18th
| Underground network | Gypsum quarries (Montmartre hill) |
|---|---|
| Mined rock | Antediluvian gypsum |
| Undermined area | Part of the 65 ha of Paris gypsum. |
| Galleries | Gypsum network. |
| Selected risk level | Moderate |
| Confidence in the classification | high |
| Nature of the ground | Montmartre hill: gypsum + Fontainebleau sands |
| Foundation issue | As gypsum is soluble, every ground investigation must verify the absence of active dissolution as well as the hill’s stability. A specific geotechnical study and monitoring of water networks are recommended. |
Sensitive areas of the 18th
- Montmartre hill, Goutte-d’Or, Clignancourt, Épinettes areas
- Gypsum quarried for plaster since the Middle Ages
Documented events in the 18th
7 August 1843
Montmartre “earthquake”
Montmartre hill (18th)
At around 1 a.m., a strong tremor was felt in Montmartre. Following an investigation, it was established that it came from a rockfall inside the underground quarries. On 19 November, a clay slip occurred on the eastern slope towards rue André-del-Sarte.
1993
Montmartre collapses
rues Audran / Constance (18th)
Cave-in on rues Audran and Constance and subsidence in cellars at the corner of rues Lepic and Tholozé. Gypsum sector of Montmartre hill.
March 2001
Collapse on rue des Martyrs
Rue des Martyrs (18th)
A gaping hole 5 m deep and 8 m long in the upper part of rue des Martyrs. The road rested on only 25 cm of ground. The last major accident for several years.
Source: Le Parisien — Beneath the cobblestones, the void (2001)
Ground, fill and clay shrink-swell
The 18th arrondissement lies on Montmartre hill: Antediluvian gypsum at depth (see quarry section), overlain by Fontainebleau sands and green marls at the summit of the hill.
As gypsum is soluble, every ground investigation must verify the absence of active dissolution as well as the hill’s stability. A specific geotechnical study and monitoring of water networks are recommended.
Unlike almost all French municipalities, inner Paris has no official mapping of the clay shrink-swell hazard (RGA). The BRGM explains this explicitly: the Paris subsoil is largely made up of reworked and artificial materials (backfill, infilled former quarries), which does not correspond to the standard methodology for this mapping — centred on detached houses, which are in the minority in Paris. This does not mean that there is no risk of differential settlement, but that no official area-by-area study exists for the capital: a ground investigation remains the only reliable way to assess a specific plot before purchase or construction.
Your steps in the 18th before a purchase or works
High gypsum risk on the Montmartre hill: IGC (Paris quarry inspectorate) consultation is essential, along with a gypsum-specific geotechnical study and checking of water networks (aggravating leaks) before purchase or works.
- IGC (Paris quarry inspectorate) information sheet — the authoritative source on the condition of the parcel’s subsoil: €10, issued within 8 days, via the City of Paris online service.
- Statutory risk statement (ERP) — mandatory for sale and letting, generated from Errial; note, it does not return cavity data in Paris.
- geotechnical survey — G1 mission before purchasing a building plot, G2 AVP before a construction or underpinning project.
- Referral to the IGC (Paris quarry inspectorate) for planning — prefectoral orders require it to be consulted for any planning permission in a quarry-risk area.
Frequently asked questions
Are there underground quarries beneath Paris’s 18th arrondissement?
Yes. The 18th arrondissement is listed in the public data of the IGC (Paris quarry inspectorate) as an area affected by the network « Gypsum quarries (Montmartre hill) », in Antediluvian gypsum. The assigned risk level is « Moderate », with high confidence in the sector’s classification. Montmartre hill and the north of the 18th were worked for gypsum (plaster). Gypsum, which is soluble in water, presents a risk of dissolution and sinkholes (fontis). Montmartre / Goutte-d’Or / Clignancourt sector.
How can I tell whether my exact address in the 18th is in an undermined area?
Quarry zoning must be read at plot level rather than arrondissement level. There are two options: the official information sheet from the IGC (Paris quarry inspectorate), at €10 and issued within 8 days, which is the legally binding source; and Sous-sol Paris’s instant pre-assessment, at €15, which matches your address against public data and immediately provides you with a readable report, including the steps to take. This pre-assessment is for information only and does not replace the IGC information sheet, the statutory risk statement (ERP), or a geotechnical study.
Why does cavity data for the 18th not appear on Géorisques?
Because for départements 75, 78, 91, 92, 93, 94 and 95, cavity data are not published on the Géorisques portal: they can be consulted with the IGC (Paris quarry inspectorate) for Paris and the inner suburbs, or with the relevant interdepartmental service. This is why a standard statutory risk statement (ERP) remains silent on Paris quarries and gypsum.
Is the 18th’s quarry risk covered by insurance?
Disorders linked to former quarries do not fall under the « natural disaster » scheme. In the event of collapse, infill works, estimated at 40 000 to 200 000 €, remain the responsibility of the owners. This is what makes checking before purchase essential.
Other arrondissements
- Subsurface of the 17th arrondissement
- Subsoil of the 19th arrondissement
- Subsoil of the 16th arrondissement
- Subsoil of the 20th arrondissement
- Subsoil of the 10th arrondissement
- See the 20 arrondissements
Sources
- City of Paris — Everything you need to know about the subsurfaces
- Wikipédia — Montmartre quarries
- DRIEAT Île-de-France — Risks related to underground cavities
- BRGM — Why is there no map of the clay shrink-swell hazard for Paris?
- Géorisques — Clay shrink-swell, 2026 version (data)
- Histories of Paris — The Montmartre earthquakes
- Le Parisien — The great quarries in the dock (2001)
- Le Parisien — Beneath the cobblestones, the void (2001)
- Géorisques — Underground cavities (data)
- City of Paris — the IGC (Paris quarry inspectorate) location
- City of Paris — Known areas of former quarries (IGC)
Page updated on 11 September 2026.