sandpit belonging to one of their own number, for the easier concealment
of their work, and for the safer removal of the quarried tufa. In such
cases the tufa may have been broken down into the condition of sand for
removal. In later times, as the catacombs were extended, the tufa dug
out from one passage was carried into the old passages no longer used;
and thus, as the catacomb extended in one direction, it was closed up in
another, and the ancient graves were concealed. This is now one of the
great impediments in the way of modern exploration; and the same process
is being repeated at present; for the Church allows none of the earth or
stone to be removed that has been hallowed as the resting-place of the
martyrs, and thus, as one passage is now opened, another has to be
closed. The archaeologists may rebel, but the priests have their way.
The ancient filling up was, however, productive of one good result; it
preserved some of the graves from the rifling to which most were exposed
during the period of the desertion of the catacombs. Most of the graves
which are now found with their tiled or marble front complete, and with
the inscription of name or date upon them unbroken, are those which were
thus secluded.

But there is still another curious fact bearing upon the Christian
origin of the catacombs. They are in general situated on somewhat
elevated land, and always on land protected from the overflow of the
river, and from the drainage of the hills. The early traditions of the
Church preserve the names of many Christians who gave land for the
purpose,--a portion of their _vignas_, or their villas. The names of the
women Priscilla, Cyriaca, and Lucina are honored with such remembrance,
and are attached to three of the catacombs. Sometimes a piece of land
was thus occupied which was surrounded by property belonging to those
who were not Christian. This seems to have been the case, for instance,
in regard to the cemetery of St. Callixtus; for (and this is one of