Introduction: Conceptualizing the Subterranean Metropolis

The entanglement of Paris’s three core subterranean systems—métro, égouts, and carrières—defies the conventional compartmentalization of infrastructural research that prioritizes single-function, bounded systems. Unlike cities such as London or New York, where underground transit, drainage, and mining infrastructure were developed incrementally by separate private or public actors with little coordination, Paris’s subterranean realm was shaped from the mid-19th century onward by a single, state-led urban modernization project: Haussmann’s renovation of the city. As historian David Pinkney noted, Haussmann’s team treated the city’s subsurface as a single “planning canvas,” where metro tunnels, sewer mains, and quarries were excavated, reinforced, and integrated in parallel, rather than as discrete, unrelated projects. This foundational difference means that any attempt to study Paris’s underground must begin with a conceptual framework capable of capturing the overlapping, co-constitutive relationships between these systems, rather than treating them as isolated objects of analysis.

Core Conceptual Definitions

To operationalize this framework, we first define three core terms that structure the entire volume: subterranean infrastructure, urban experience, and the social life of infrastructural systems. Each term moves beyond conventional technical definitions to center the political, social, and cultural dimensions of underground space that have been overlooked in most existing scholarship.

Subterranean Infrastructure: Materiality and Symbolism in Tension

For the purposes of this study, subterranean infrastructure refers to the full assemblage of human-made, purpose-built systems located below the earth’s surface in the Paris metropolitan region, including but not limited to transit tunnels, sewer networks, mining voids, utility conduits, and defensive bunkers. This definition intentionally rejects narrow technical framings that limit infrastructure to “large-scale technical systems” serving public utility functions, as such definitions erase the informal, non-functional, and symbolic dimensions of underground space. For example, the Paris Catacombs—originally a solution to the city’s 18th-century cemetery overcrowding crisis, and later a storage site for municipal archives and resistance fighters during World War II—are now a global cultural icon and tourist destination, visited by more than 500,000 people annually. While they do not serve a conventional “public utility” function, they are an integral part of the city’s subterranean infrastructural landscape, shaped by the same geological, political, and economic forces that produced the metro and sewer systems.

This definition also centers the *material agency* of subterranean infrastructure, drawing on the work of infrastructure studies scholars such as Brian Larkin and Stephen Graham, who argue that infrastructure is not a passive backdrop to social life, but an active shaper of human and non-human interactions. The limestone bedrock that underlies most of central Paris, for example, is both a resource that enabled the construction of the city’s iconic above-ground landmarks (including Notre-Dame and the Louvre) and a constraint that has shaped every subterranean project since the Roman era: its soft, porous nature makes it prone to collapse when excavated, requiring constant reinforcement that has added billions of euros in construction costs over the past 200 years. This material constraint has, in turn, shaped the city’s above-ground urban form: Haussmann’s wide boulevards were in part designed to accommodate the ventilation shafts and access points needed for the sewer and metro systems, while the high cost of building deep tunnels in limestone has meant that most of the Paris metro is located no more than 20 meters below the surface, a shallowness that has created unique challenges for flood mitigation during extreme weather events.

Urban Experience: The Subterranean as a Site of Everyday Life

The second core concept, urban experience, refers to the embodied, sensory, and social interactions that Parisians and visitors have with the city’s underground space, ranging from the mundane (a daily commute on the metro, a trip to a basement grocery store) to the extraordinary (a secret concert in a disused quarry, a tour of the Catacombs). This definition builds on the work of urban studies scholars such as Henri Lefebvre and Michel de Certeau, who argued that urban space is produced through the everyday practices of its inhabitants, rather than being a static product of top-down planning. The Paris underground is a particularly rich site for studying this process, because its spaces have been used for such a wide range of purposes over time: the same sewer tunnel that carried wastewater in the 19th century was used as a secret weapons factory by the French Resistance during World War II, and later as a venue for underground raves in the 1990s.

Recent research on “subterranean urbanism” has highlighted how underground spaces can both reproduce and challenge existing power relations. For example, the metro’s uniform fare structure, introduced in 1900, was designed to enable working-class Parisians to commute from the newly built affordable housing in the city’s periphery to jobs in the central business district, effectively subsidizing working-class mobility in ways that transformed the city’s social geography. At the same time, the metro’s design—including its narrow staircases, lack of elevators in many older stations, and high fares for single tickets—has created barriers to mobility for disabled people, low-income residents without monthly passes, and parents with strollers, reproducing existing inequalities above ground. Similarly, the city’s network of underground quarries has been used as a site of informal housing for undocumented migrants since the 1990s, with an estimated 200 people living in disused quarry tunnels near the Porte de Clignancourt as of 2023, according to data from the Paris municipal homeless services agency. These examples illustrate how the subterranean is not a neutral space, but a site where struggles over access, equity, and belonging are constantly being negotiated.

The Social Life of Infrastructural Systems

The third core concept, the social life of infrastructural systems, draws on actor-network theory (ANT) and the “new materialist” turn in social theory to frame infrastructure as an active, non-human actor in urban social relations, rather than a passive tool of human governance. This perspective rejects the conventional narrative of infrastructural development as a linear process of human planning, construction, and operation, instead highlighting how infrastructure shapes, and is shaped by, the social, political, and economic contexts in which it is embedded.

In the Paris case, this framework allows us to trace how the three subterranean systems have acted as agents of urban transformation in three distinct but interrelated ways. First, their material properties have constrained and enabled specific forms of urban development: the shallow depth of the metro system, for example, has made it vulnerable to flooding during extreme rainfall events, a problem that has become more acute in recent decades due to climate change, leading the RATP (the Paris transit authority) to invest more than €1 billion in flood mitigation infrastructure between 2015 and 2023. Second, their operational logics have reshaped social relations: the sewer system’s 24/7 maintenance requirements have created a distinct, highly unionized workforce that has played a key role in French labor politics since the late 19th century, including a major strike in 1889 that forced the national government to negotiate a national public works labor agreement just weeks before the opening of the 1889 Exposition Universelle. Third, their cultural representations ha