re formerly,
outside the walls, as burial was not allowed within city limits. To
explain their origin and to understand their significance we must bear
in mind the following rules. The action of the Roman law towards the
Christians, that is, towards persons accused of atheism and rebellion
against the Empire, resulted in the execution of those who were
convicted. Except in extraordinary cases, the body of the victim could
be claimed by relatives and friends and buried with due honors. In
chapters vi. and vii. instances will be quoted of the erection of
imposing tombs to the memory of Roman patricians, generals and
magistrates, who were put to death under the imperial regime. The same
privileges of burial were granted to the Christians, who preferred,
however, the modesty and safety of a grave in the heart of the
catacombs to the pompous luxury of a mausoleum above ground. The grave
of a martyr was an object of consideration, and was often visited by
pilgrims, who adorned it with wreaths and lights on the anniversary of
his execution. After the end of the persecutions the first thought of
the victorious church was to honor the memory of those who had fought
so gallantly for the common cause, and who at the sacrifice of their
lives had hastened the advent of the days of freedom and peace. No
better altar than those graves could be chosen for the celebration of
divine service; but they were sunk deep in the ground, and the
cubicula of the catacombs were hardly capable of containing the
officiating clergy, much less the multitudes of the faithful. Touching
the graves, removing them to a more suitable place, was out of the
question; in the eyes of the early Christians no more impious
sacrilege could be perpetrated. There was but one way left to deal
with the difficulty; that of cutting away the rock over and around the
grave, and thereby gaining such space as was deemed sufficient for the
erection of a basilica. The excavation was done in conformity with two
rules,--that the tomb of the martyr should occupy the place of honor
in the middle of the apse, and that the body of the church should be
to the _east_ of the tomb, except in cases of "force majeure," as when
a river, a public road, or some other such obstacle made it necessary
to vary this principle.

Such is the origin of the greatest sanctuaries of Christian Rome. The
churches of S. Peter on the Via Cornelia, S. Paul on the Via
Ostiensis, S. Sebastian on the Via Appi