Mines Of Tunnel Network, Catacombes De Paris, Paris, France

Paris' earliest burial grounds were to the southern outskirts of the Roman-era Left Bank city. In ruins after the Roman empire's 5th-century fall and the ensuing Frankish invasions, Parisians eventually abandoned this settlement for the marshy Right Bank: from the 4th century, the first known settlement there was on higher ground around a Saint-Etienne church and burial ground (behind today's Hôtel de Ville), and Right Bank urban expansion began in earnest after other ecclesiastical landowners filled in the marshlands from the late 10th century. Thus, instead of burying its dead away from inhabited areas as per usual human customs, the Paris Right Bank settlement began its life with cemeteries at its very centre.
The most central of these cemeteries, a burial ground around the 5th-century Notre-Dame-des-Bois church, became the property of the Saint-Opportune parish after the original church was demolished by the 9th-century Norman invasions. When it became its own parish under the "Saints Innocents" church from 1130, this burial ground, filling the land between today's rue Saint-Denis, rue de la Ferronnerie, rue de la Lingerie and the rue Berger, had become the City's principal cemetery.
By the end of the same century "Saints Innocents" was neighbour to the principal Parisan Les Halles marketplace, and already filled to overflowing. To make room for more burials, the long-dead were exhumed and their bones packed into the roofs and walls of "charnier" galleries built to the inside of the cemetery walls. By the end of the 18th century, the central burial ground was a two metre high mound of earth filled with centuries of Parisian dead from disease, famine, and wars, plus the remains from the Hôtel-Dieu hospital and the Morgue; other Parisian parishes had their own burial grounds, but the conditions in Les Innocents cemetery were by far the worst.
A series of ineffective decrees limiting the use of the cemetery did little to remedy the situation, and it was not until the late 18th century that it was decided to create three new large-scale suburban burial grounds on the outskirts of the city, and to condemn all existing parish cemeteries within city limits.