relics shall be contained
within an altar before it is held to be consecrated, probably began.
Perhaps it was with some reference to that portion of the Apocalypse in
which St. John says, "I saw under the altar the souls of them that were
slain for the word of God, and for the testimony which they held. And
they cried with a loud voice, saying, How long, O Lord, holy and true,
dost thou not judge and avenge our blood on them that dwell on the
earth? And white robes were given unto every one of them; and it was
said unto them, that they should rest yet for a little season, until
their fellow-servants also and their brethren that should be killed as
they were should be fulfilled."[G] At any rate, these words must have
dwelt in the memories of the Christians who came to worship God in the
presence of the dead by whom they were surrounded in the catacombs. But
they knelt before the altar-tombs, not as before altars consecrated with
relics of saints, but as before altars dedicated to God and connected
with the memory of their own honored and beloved dead, whom he had
called from them into his holy presence.

[Footnote F: These chapels are generally about ten feet square. Some are
larger, and a few smaller than this.]

[Footnote G: Revelations, vi. 9-11. It seems probable that another
custom of the Roman Church took its rise in the catacombs,--that of
burning candles on the altar; a custom simple in its origin, now turned
into a form of superstition, and often abused to the profit of priests.]

It is impossible to ascertain the date at which these chapels were first
made; probably some time about the middle of the second century they
became common. In many of the catacombs they are very numerous, and it
is in them that the chief ornaments and decorations, and the paintings
which give to the catacombs an especial value and importance in the
history of Art, and which are among the most interesting illustrations
of the state of religious feeling and belief in the early centuries, are
found. Some of the chapels are known to be of comparatively late date,
of the fourth and perhaps of the fifth century. In several even of
earlier construction is found, in addition to the altar, a niche cut out
in the rock, or a ledge projecting from it, which seems to have been
intended to serve the place of the credence table, for holding the
articles used in the service of the altar, and at a later period for
receiving the elements before they