Descending from the level of the ground by a flight of steps into one of the narrow underground passages, one sees on either side, by the light of the taper with which he is provided, range upon range of tombs cut, as has been described, in the walls that border the pathway.  Usually the arrangement is careful, but with an indiscriminate mingling of larger and smaller graves, as if they had been made one after another for young and old, according as they might be brought for burial.  Now and then a system of regularity is introduced, as if the fossor, or digger, who was a recognized officer of the early Church, had had the leisure for preparing graves before they were needed.  Here, there is a range of little graves for the youngest children, so that all infants should be laid together, then a range for older children, and then one for the grown up.  Sometimes, instead of a grave suitable for a single body, the excavation is made deep enough into the rock to admit of two, three, or four bodies being placed side by side,—­family graves.  And sometimes, instead of the simple loculus, or coffin-like excavation, there is an arch cut out of the tufa, and sunk back over the whole depth of the grave, the outer side of which is not cut away, so that, instead of being closed in front by a perpendicular slab of marble or by tiles, it is covered on the top by a horizontal slab.  Such a grave is called an arcosolium, and its somewhat elaborate construction leads to the conclusion that it was rarely used in the earliest period of the catacombs[E].  The arcosolia are usually wide enough for more than one body; and it would seem, from inscriptions that have been found upon their covering-slabs, that they were not infrequently prepared during the lifetime of persons who had paid beforehand for their graves.  It is not improbable that the expenses of some one or more of the cemeteries may have been borne by the richer members of the Christian community, for the sake of their poorer brothers in the faith.  The example of Nicodemus was one that would be readily followed.

[Footnote E:  There is one puzzling circumstance in the cemetery of S. Domitilla. All the graves in this cemetery are arcosolia, and yet the date of construction is early.  The Cavaliere de Rossi suggests that the cemetery was begun at the expense of the Domitilla whose name it bears, the niece of Domitian, previously to her banishment; that her position enabled her to have it laid out from the beginning on a regular plan, and to introduce this more expensive and elaborate form of grave, which was continued for the sake of uniformity in the later excavations.]