The different phases of expansion of Paris have required during all its history the exploitation of local careers. In the beginning (at the Roman time), it was obiously only open-sky careers. It is necessary to wait for the end of the tenth century and therefore a new flight of construction, Hugues Capet having made of Paris the new capital of his kingdom, to see the first underground careers to appear. The exploitation has taken an industrial dimension since the 12th and 13th centuries, notably for the construction, under Philippe Auguste, of ramparts protecting the city, of the Notre-Dame cathedral, of the royal fortress of the Louvre (of which we can still admire the foundations) and of Covered markets. It is from this period that dates, for example, the careers of the Val de Grâce hospital (and therefore of the Z room).
Emptiness thus created in the subsoil were little by little forgotten: the wells of extraction have been filled to avoid accidents or have been used like discharges. It is only at the 18th century, after a set of downfalls (fontis) that authorities take into account the danger that represents the Parisian subsoil. On April 4, 1777 is created the Inspection Générale des Carrières, which has to list and to strengthen forever the careers of Paris.
Teams of the IGC
will, during more than 200 years, make of the careers of Paris one of the most
important architectural complex of France, and give them the aspect that we know
now. It is nowadays relatively rare to find a wall that is older than the 18th
century. In general, only ceilings are original.
Some people don't hesitate to see in consolidations established by Guillaumot,
who was the first general inspector of careers, Héricart de Thury and Trémery,
something else than good work and the application of the architectural norms.
A famous architect
also let his mark in the careers: Mansard. He was charged by the queen, Anne
d'Autriche, to build a church and an abbey (to thank God for the birth of her
son, the future Louis XIV) that one named since Val-de-Grâce. While digging to
establish the foundations of the future building, he discovered incredible emptinesses
in the subsoil and had to strengthen it before building anything. This work,
given its importance, took time and money. Wondering about the weak advancement
of the work, the queen fired Mansard, whereas he had just finished the construction
of the first floor.
It is the reason why some people say that the most beautiful construction of
Mansard at the Val-de-Grâce is under ground.
It currently remains
770 hectares of emptiness resulting of these old careers, that makes a volume
of six millions cubic meters.
Galleries can be of two types. There are first 135 kilometers of galleries of
inspection: 91 under streets and 44 under gardens and other public buildings.
These galleries are regularly inspected by the IGC. It is necessary to know that
the IGC takes in charge only the consolidation of galleries under the public
domain. The consolidation of emptinesses under private properties is to be done
by the owners. Besides, 150 kilometers of galleries subsist under private domains.
All in all, almost 300 kilometers (twice the length of all the subway lines).
Inspection galleries are mainly under the left bank of the Seine: