[NYer]

Partial view of the presbytery with the palimpsest wall in the centre. On all walls of the presbytery there are plasters belonging to a late antique decoration of the monument, on which were applied wall paintings at different periods. In the foreground, the early medieval flooring in Opus Alexandrinum is visible.
(Notice the altar design and position)

Additional Resources:

History from antiquity until the year 847 A.D.
Santa Maria Antiqua

[B Knotts]

I'm guessing that altar is the work of the "restorers?"

[Victoria Delsoul]

Thanks so much for the info and for posting these wonderful photos.