The Salpêtrière was originally a gunpowder factory ('salt peter' being a constituent of gunpowder). In 1669 Bruand Bruant succeeded Pierre Le Muet as director of works at the Hôpital de la Salpêtrière, which had been founded by Cardinal Jules Mazarin in 1656 on the outskirts of Paris to house mendicants and others. It served as a prison for prostitutes, and a holding place for the mentally disabled, criminally insane, epileptics, and the poor. The following year Bruand began construction of its domed, centrally planned chapel, St .Louis de la Salpêtrière. Four rectangular naves forming a Greek cross radiate from its octagonal crossing. The Pitié-Salpêtrière is now a general teaching hospital with departments focusing on most major medical specialities.