By the end of the 18th century, overcrowded cemeteries in Paris had become a medical problem and city officials began to use the catacombs beneath the streets as a massive burial ground. By 1810 the "city of the dead" had opened to the public and artists soon followed, generating a new interest in the macabre. Although the prefect of Paris officially closed the catacombs to the public in 1830, lovers of the bizarre periodically gained access to the subterranean vaults. Known primarily for his portraiture, Nadar made this photograph of the ghoulish d矇cor with an artificial light of his own design, an early arc lamp known as a Serrin Regulator. The Catacombs of Paris are underground ossuaries. The ossuaries holds the remains of about six million people and fills a renovated section of caverns and tunnels that are the remains of historical stone mines.