A mass grave is a grave containing multiple number of human corpses, which may or may not be identified prior to burial. There is no strict definition of the minimum number of bodies required to constitute a mass grave, although the United Nations defines a mass grave as a burial site which contains three or more victims of execution.
Mass graves are an infamous variation on common burial, still occasionally practiced today under normal circumstances. Mass or communal burial was a common practice before the development of a dependable crematory chamber by an Italian named Brunetti in 1873.
In Paris, the practice of mass burial, and in particular, the condition of the infamous Cimetière des Innocents, led Louis XVI to eliminate Parisian cemeteries. The remains were removed and placed in the Paris underground forming the early Catacombs. La Cimetière des Innocents alone had 6,000,000 dead to remove. Burial commenced outside of the city limits in what is now Père Lachaise cemetery.
Mass graves are usually created after a large number of people die or are killed, and there is a desire to bury the corpses quickly for sanitation concerns. In disasters, mass graves are used for infection and disease control.