The literary industry of this pioneer explorer was immense. He carefully examined all the Latin, Greek, and Oriental Fathers; all the ecclesiastical records, canons, and decrees of councils; the lives of the saints, the acts of the martyrs--everything, in fact, which could illustrate the history of the Catacombs and of the early church. The result of these labours is seen in the bulky MS. volumes, of many thousand pages, written with his own hand, which are still extant in the Oratorian Library at Rome. He was not permitted to see the publication of his great work, in which was disclosed to the world the wonderful _terra incognita_ lying so long hidden beneath the busy life of the Eternal City, but died while writing the last chapter. It was too valuable a contribution to Christian archæology, however, to remain unpublished, and it was given to the world, under the appropriate title of “Subterranean Rome,”[262] in the year 1632, or five years after its author’s death. This book contains an admirable topographical account of each cemetery which he had explored, taking in order the great consular roads leading from the city. Bosio’s attempted identification of the cemeteries and principal tombs and shrines described in the ancient 154 ecclesiastical records is not always sufficiently accurate. He is rather uncritical and confused in his arrangement, although honest and, in matters of personal observation, exact. His work is of great value as giving an account of many crypts and monuments, and copies of many paintings which have perished through the decay or vandalism of the last two hundred years, or whose position has been forgotten. Among these is the Jewish Cemetery before mentioned, of which no evidence is extant save Bosio’s description. His name, written in his own peculiarly bold style, is met with in many of the newly opened galleries of the Catacombs, showing that he had previously explored those parts since filled with earth. Many objects of priceless value have been lost since Bosio’s day by the desultory and unsystematic excavations of private and independent explorers. These were conducted, not upon a system of enlightened archæological research, but upon mere caprice; and were guided too often by a superstitious zeal for the identification and translation of the relics of the saints, or by the more sordid motive of trafficking in their remains, or of pillaging the gold and silver with which some of the more illustrious shrines were still adorned. In this quest many paintings, sculptures, and inscriptions were destroyed or defaced of which no record has been preserved. After the year 1688 the excavations were pursued under pontifical supervision, though often neglected through indifference or embarrassed by want of funds.