When inhumation was introduced, at first small modifications in the columbarium appeared.
The walls, at floor level, obtained recesses for burials. Most of these recesses are arc-shaped and called arcosolia.
Later on, small niches were replaced by arcosolia and in new tombs the number of arcosolia increased. After the early third century AD new tombs were designed for inhumation only. Because arcosolia are uneconomic in space, soon the area underneath the floor was also used. The floor was divided by brick walls into a series of graves,
called formae, sometimes one row on top of another.
The style of decoration too changed. There was more space to decorate, and scenes of hunting, wgardens with cupids and so on became common.
The kind of inhumation too depended on the wealth of the family.
Many bodies were laid in a plain terracotta sarcophagus. Those who could afford it were laid in a sarcophagus made of marble, simple or elaborated. The majority were laid in the arcosolia or formae without a sarcophagus. The arcosolium itself was closed by a rough wall, sometimes plastered, imitating marble, or by a marble slab. The latter are plain or decorated. Formae were often covered by the mosaic or marble floor of the burial chamber.