Rome has an extensive amount of ancient catacombs, or underground burial places under or near the city, of which there are at least forty, some discovered only in recent decades. Though most famous for Christian burials, they include pagan and Jewish burials, either in separate catacombs or mixed together. The first large-scale catacombs were excavated from the 2nd century onwards. Originally they were carved through tuff, a soft volcanic rock, outside the boundaries of the city, because Roman law forbade burial places within city limits. Currently, maintenance of the catacombs is in the hands of the Papacy which has invested in the Salesians of Don Bosco the supervision of the Catacombs of St. Callixtus on the outskirts of Rome.