The priest was at the evening office, the stone lid of a martyr's tomb placed under an arched vault (arcosolium) serving as altar.
First, the arcosolium is not exclusively Christian in character.
However, all tombs of this period fall into two groups, kk tombs and arcosolium tombs.
In arcosolium tombs the receptacles are benches cut in the wall, like the berths in a steamer's cabin.
Other forms of very frequent recurrence are the table tomb and arched tomb, or arcosolium.
Each side of the cubiculum, except that of the entrance, usually contains a recessed tomb, either a table-tomb or an arcosolium.
The front of the arcosolium is closed by a wall, on the surface of which is an interesting fresco, which is here reproduced.
A peculiar form of grave common in these chambers, as well as in the galleries, is that known as the arcosolium, or arched tomb.
The arcosolium to which this is attached contains the remarkable paintings represented in the accompanying engraving.