indications of the character of the occupants of these burial-places
prove that they were Christian.[D] They are very different from the
sepulchres of the great and rich families of Rome, who lined the Appian,
the Nomentan, and Flaminian Ways with their tombs, even now magnificent
in ruin; very different, too, from the _columbaria_, or pigeon-holes,
in which the ashes of the less wealthy were packed away; and still more
different from the sad undistinguished ditch that received the bodies of
the poor:--

"Hoc miserae plebi stabat commune sepulcrum."

[Footnote D: The volcanic rocks are the _Tufa litoide_, very hard, and
used for paving and other such purposes; difficult to be quarried, and
unfit for graves on account of this difficulty. The _Tufi granulare_, a
soft, friable, coarse-grained rock, easily cut,--fitted for excavation.
It is in this that the catacombs are made. It is used for very few
purposes in Rome. One may now and then see some coarse filling-up of
walls done with it, or its square-cut blocks piled up as a fence. The
third is the _Pura pozzolana_,--which is the _Tufa granulare_ in a state
of compact sand, yielding to the print of the heel, dug like sand, and
used extensively in the unsurpassed mortar of the Roman buildings.]

It not unfrequently happens in the soil of the Campagna, that the vein
of harder rock in which the catacombs are quarried assumes the soft and
sandy character which belongs to it in a state of decomposition. The
ancient Romans dug this sand as the modern Romans do; and it seems
probable, from the fact that some of the catacombs open out into
_arenaria_, or sandpits, as in the case of the famous one of St. Agnes,
that the Christians, in time of persecution, when obliged to bury with
secresy, may have chosen a locality near some disused sandpit, or near a