quarry; so that while one entrance was carefully
watched, the pursued might escape in a totally different direction by
another. But, to quote J.H. Parker, "the catacombs were never intended,
nor fit for, dwelling-places, and the stories of persons living in them
for months are probably fabulous. According to modern physicians it is
impossible to live many days in the caves of _pozzolana_ in which many
of the catacombs are excavated." Equally exaggerated are the statements
as to the linear and lateral extent of the catacombs, and their
intercommunication with one another. Without resorting to this
exaggeration, Mommsen can speak with perfect truth of the "enormous
space occupied by the burial vaults of Christian Rome, not surpassed
even by the _cloacae_ or sewers of Republican Rome," but the data are
too vague to warrant any attempt to define their dimensions. Marchi has
estimated the united length of the galleries at from 800 to 900 m., and
the number of interments at between 6,000,000 and 7,000,000; Martigny's
estimate is 587 m.; and Northcote's, lower still, at "not less than 350
m." The idea of general intercommunication is negatived by the fact that
the chief cemeteries are separated by low ground or valleys, where any
subterranean galleries would be at once filled with water.

It now remains to speak of the history of these subterranean
burial-places, together with the reasons for, and mode of, their
construction. From the period of the rediscovery of the catacombs in the
16th century till comparatively recent times a gigantic fallacy
prevailed, repeated by writer after writer, identifying the Christian
burial-places with disused sand-pits. It was accepted as an
unquestionable fact by every one who undertook to describe the
catacombs, that the Christians of Rome, finding in the labyrinthine
mazes of the exhausted _arenariae_, which abounded in the environs of
the city, whence the sand used in building had been extracted, a
suitable place for the interment of their martyred brethren, where also
the sacred rites accompanying the interment might be celebrated without
fear of interruption, took possession of them and used them as
cemeteries. It only needed a comparison of the theory with the visible
facts to refute it at once, but nearly three centuries elapsed before
the independence of the _arenariae_ and the catacombs was established.
The discovery of this independence is due to Marchi. Starting with the
firmest bel