The Paris Catacombs are a network of underground tunnels and chambers beneath the streets of Paris, originally quarries that were repurposed into an ossuary in the late 18th century to alleviate cemetery overcrowding. The most notable and large-scale transfer took place in 1786, during the reign of Louis XVI, when the city's graveyards were emptied. They hold the skeletal remains of over six million people who lived between the 12th and 18th centuries, arranged decoratively in walls and patterns. Today, the catacombs attract tourists, though much of the labyrinthine tunnels remain off-limits due to safety concerns.