The Catacombs of Paris (French: Catacombes de Paris, about this are underground ossuaries in Paris, France, which hold the remains of more than six million people in a small part of a tunnel network built to consolidate Paris' ancient stone quarries. Extending south from the Barrière d'Enfer ("Gate of Hell") former city gate, this ossuary was created as part of the effort to eliminate the city's overflowing cemeteries. Preparation work began not long after a 1774 series of gruesome Saint Innocents-cemetery-quarter basement wall collapses added a sense of urgency to the cemetery-eliminating measure, and from 1786, nightly processions of covered wagons transferred remains from most of Paris' cemeteries to a mine shaft opened near the Rue de la Tombe-Issoire. The ossuary remained largely forgotten until it became a novelty-place for concerts and other private events in the early 19th century; after further renovations and the construction of accesses around Place Denfert-Rochereau, it was open to public visitation from 1874. Since 2013, the Catacombs number among the 14 City of Paris Museums managed by Paris Musées. Although the ossuary comprises only a small section of the underground "carrières de Paris" ("quarries of Paris"), Parisians currently often refer to the entire tunnel network as the catacombs. Paris' earliest burial grounds were to the southern outskirts of the Roman-era Left Bank city. In ruins after the Western Roman Empire's 5th-century end 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 the present Hôtel de Ville), and urban expansion on the Right Bank 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 usual, the Paris Right Bank settlement began with cemeteries near its 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 associated with the church of the "Saints Innocents" from 1130, this burial ground, filling the land between the present 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 Parisian marketplace Les Halles, 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 inside the cemetery walls. By the end of the 18th century, the central burial ground was a two-metre-high (6.6 ft) mound of earth filled with centuries of Parisian dead, 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 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.